Onchange event does not fire sometimes in Forms

Hi

I have some js functions in my forms, that fire when a field changes. But these functions does not work something. I even put a "deubbger" and used browser developer tools to see if the code reaches to the function, but it seems it does not call it at all.

Is there any reason for that ? I have spent lots of time with many browsers but have not got any solution. The wonderful thing is that it happens in Dynamics CRM 2015, and I have never seen it in 2011 Version.