Django compatibility is messed up with Python

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Python

form

Django

i have no idea what happen to django ,
i am using django 1.8.6 and with python 3.5.2
i am working on form's and the form's validation like field validation work's well but i noticed the validation error for empty field was'nt rasing an error, by default django set required field to True , and so it should raise an error , but the funny part was i have two form, and what i tried was,

What I have tried:

i actually tried upgrading django to version 1.11 latest, and when i checked the form's it started working the empty field raised an validation error by default without touching to code ' and then i checked the second form which was still the same no empty validation error !....

the confusion is why django form automatically started working upon upgrading to 1.11 with the same python version 3.5.2 and with same code , and why the second form did'nt worked while the first one did !

if there's a compatibilty issue im facing then why custom clean_ method also does'nt work neither ' error_messages' attribute.