diff --git a/render-app/src/test/java/org/janelia/alignment/RenderTransformMeshMappingWithMasksTest.java b/render-app/src/test/java/org/janelia/alignment/RenderTransformMeshMappingWithMasksTest.java
new file mode 100644
index 000000000..e4c992826
--- /dev/null
+++ b/render-app/src/test/java/org/janelia/alignment/RenderTransformMeshMappingWithMasksTest.java
@@ -0,0 +1,63 @@
+package org.janelia.alignment;
+
+import ij.process.ImageProcessor;
+
+import mpicbg.trakem2.transform.TransformMeshMappingWithMasks;
+
+import org.janelia.alignment.util.ImageProcessorCache;
+import org.junit.Assert;
+import org.junit.Test;
+
+import static org.janelia.alignment.Renderer.renderImageProcessorWithMasks;
+
+/**
+ * Tests the {@link RenderTransformMeshMappingWithMasks} class.
+ */
+public class RenderTransformMeshMappingWithMasksTest {
+
+    @Test
+    public void testMap() {
+        // TODO: uncomment below to run test
+        // renderProblemArea();
+
+        // one way to "solve" problem is to revert RenderTransformMeshMappingWithMasks to commit just before
+        // Tobias' December 2024 / January 2025 changes: 25bcdd4cecac5baace30997d950793c82a65e832
+    }
+
+    @SuppressWarnings("unused")
+    private static void renderProblemArea() {
+
+        // notes:
+        //   a) w61_s109_z12_problem_a.json has the tile order flipped in descending tileId order
+        //      because I noticed a black line when I was working on something else.
+        //      I don't think the descending order has anything to do with the source problem,
+        //      other than where it shows up.
+        //   b) repo path is render-app/src/test/resources/stitch-test/w61_s109_z12_problem_a.json
+
+        final RenderParameters renderParameters =
+                RenderParameters.loadFromUrl("src/test/resources/stitch-test/w61_s109_z12_problem_a.json");
+
+        final TransformMeshMappingWithMasks.ImageProcessorWithMasks worldTarget =
+                renderImageProcessorWithMasks(renderParameters, ImageProcessorCache.DISABLED_CACHE);
+        final ImageProcessor ip = worldTarget.ip;
+
+        boolean foundZeroPixel = false;
+        for (int y = 0; y < ip.getHeight(); y++) {
+            for (int x = 0; x < ip.getWidth(); x++) {
+                final int pixel = ip.getPixel(x, y);
+                if (pixel == 0) {
+                    foundZeroPixel = true;
+                }
+                System.out.printf("%4d", pixel);
+            }
+            System.out.println();
+        }
+
+        if (foundZeroPixel) {
+            // TODO: uncomment below and break on Assert.fail call to see pixels in IDE
+            // final BufferedImage bi = ip.getBufferedImage();
+            Assert.fail("found zero pixel in rendered image");
+        }
+
+    }
+}
diff --git a/render-app/src/test/resources/stitch-test/w61_s109_z12_m0009_sfov_090.png b/render-app/src/test/resources/stitch-test/w61_s109_z12_m0009_sfov_090.png
new file mode 100644
index 000000000..d633d3fdc
Binary files /dev/null and b/render-app/src/test/resources/stitch-test/w61_s109_z12_m0009_sfov_090.png differ
diff --git a/render-app/src/test/resources/stitch-test/w61_s109_z12_m0015_sfov_074.png b/render-app/src/test/resources/stitch-test/w61_s109_z12_m0015_sfov_074.png
new file mode 100644
index 000000000..8e66fe78e
Binary files /dev/null and b/render-app/src/test/resources/stitch-test/w61_s109_z12_m0015_sfov_074.png differ
diff --git a/render-app/src/test/resources/stitch-test/w61_s109_z12_problem_a.json b/render-app/src/test/resources/stitch-test/w61_s109_z12_problem_a.json
new file mode 100644
index 000000000..70c07309a
--- /dev/null
+++ b/render-app/src/test/resources/stitch-test/w61_s109_z12_problem_a.json
@@ -0,0 +1,102 @@
+{
+  "meshCellSize": 64,
+  "minMeshCellSize": 0,
+  "x": 48200,
+  "y": 59300,
+  "width": 4,
+  "height": 5,
+  "scale": 1,
+  "areaOffset": false,
+  "convertToGray": false,
+  "quality": 0.85,
+  "numberOfThreads": 1,
+  "skipInterpolation": false,
+  "binaryMask": false,
+  "excludeMask": false,
+  "doFilter": false,
+  "addWarpFieldDebugOverlay": false,
+  "fillWithNoise": false,
+  "tileSpecs": [
+    {
+      "tileId": "w61_magc0145_scan015_m0015_r14_s74",
+      "layout": {
+        "sectionId": "12.0",
+        "imageRow": 51,
+        "imageCol": 51,
+        "stageX": -36545.27105209528,
+        "stageY": -13410.214592926066
+      },
+      "z": 12,
+      "minX": 48103,
+      "minY": 58051,
+      "maxX": 50107,
+      "maxY": 59799,
+      "width": 2000,
+      "height": 1748,
+      "minIntensity": 0,
+      "maxIntensity": 255,
+      "mipmapLevels": {
+        "0": {
+          "imageUrl": "src/test/resources/stitch-test/w61_s109_z12_m0015_sfov_074.png"
+        }
+      },
+      "transforms": {
+        "type": "list",
+        "specList": [
+          {
+            "type": "leaf",
+            "className": "org.janelia.alignment.transform.ExponentialFunctionOffsetTransform",
+            "dataString": "3.164065083689898,0.010223592506552219,0.0,0"
+          },
+          {
+            "type": "leaf",
+            "className": "mpicbg.trakem2.transform.AffineModel2D",
+            "dataString": "1.0 0.0 0.0 1.0 48106.65601272403 58051.74176269165"
+          }
+        ]
+      },
+      "meshCellSize": 64
+    },
+    {
+      "tileId": "w61_magc0145_scan015_m0009_r70_s90",
+      "layout": {
+        "sectionId": "12.0",
+        "imageRow": 50,
+        "imageCol": 50,
+        "stageX": -36840.73885339055,
+        "stageY": -14313.184546360093
+      },
+      "z": 12,
+      "minX": 47842,
+      "minY": 57554,
+      "maxX": 49846,
+      "maxY": 59302,
+      "width": 2000,
+      "height": 1748,
+      "minIntensity": 0,
+      "maxIntensity": 255,
+      "mipmapLevels": {
+        "0": {
+          "imageUrl": "src/test/resources/stitch-test/w61_s109_z12_m0009_sfov_090.png"
+        }
+      },
+      "transforms": {
+        "type": "list",
+        "specList": [
+          {
+            "type": "leaf",
+            "className": "org.janelia.alignment.transform.ExponentialFunctionOffsetTransform",
+            "dataString": "3.164065083689898,0.010223592506552219,0.0,0"
+          },
+          {
+            "type": "leaf",
+            "className": "mpicbg.trakem2.transform.AffineModel2D",
+            "dataString": "1.0 0.0 0.0 1.0 47845.959522659396 57554.743480678524"
+          }
+        ]
+      },
+      "meshCellSize": 64
+    }
+  ],
+  "minBoundsMeshCellSize": 64
+}
\ No newline at end of file