Hello,
I am not 100% sure that this is an mIRC bug, because i am using an Windows 10 yet and i had not the time to test it into an other machines, but as i saw is that if i enter an incorrect loop the mIRC will stuck as supposed and if i will press the Ctrl+Break it will get back normal, but here is something strange that if i enter an loop and i will count up to 10 and double or triple click into the mIRC and the mIRC will get into the Not Responding mode then if i will press the Ctrl+Break button the mIRC will ignore it and will not break out in result to force the mIRC to stuck, i had take an small video to try to explain this strange issue.
mIRC 7.41 beta3
Video:
https://goo.gl/Ppe506- Thanks!