The acceptance check result of last time remains.

[idatte2018]

Once you check "I agree" to ON and Sumit it In the validation example page, backbone validation will remember the success result. Because there is some errors with other input element, if you modify them and check "I agree" to OFF, you will sumit it successfully without error because there is not checkbox value in model data and backbone validation use last check result of acceptance.

http://jsfiddle.net/thedersen/udXL5/

[eparisio]

i think the problem is on how you input the value in the set() method. Probably when you input the form you use a val() function. stackoverflow -similar- problem example