I am not sure what you mean by 'this bug'.  I presume by 'take input' you mean 'display keystrokes on the input line'.  If so, the behavior you describe for 3.6 is the correct behavior and not a bug: accept kestrokes until 'Enter' is pressed or until the process awaiting input is killed.  F5 kills the current user code execution process, as opposed to the IDLE GUI interaction process, and starts a new one.  That is what 'Restart' means.

Experimenting with IDLE on 3.5 and 3.6 on Windows 10, I experienced the (correct) behavior described above.  It does not make any difference whether there was any unsent input before hitting F5 or not.  I did not notice any difference between the two versions.  In both, hitting 'Enter' terminates input.

Unless you can provide more details that convince me otherwise, I will close this as 'not a bug'.