Why don't input masks work on forms encrypted with keys I personally created?

I have a test form that I encrypted with my own public key (created in PuttyGen). When I try to put an input mask on the serial number form, the input mask does not work at all. Is this a bug or limitation? 

It seems that the Input Mask is not working because of some glitch. I cloned your form and I was able to replicate the same issue. On my cloned form I was able to resolve the issue by turning off form encryption and turning it back on. Please try the same with your form. Set Encrypt Form Data option to No and then set it back to Yes. You should use your existing key. 

https://form.jotform.com/80234721240949 

Here is my form: https://form.jotform.com/80234721240949 

Feel free to test it. You can also clone it. 

Hope this helps to solve the issue.