I'm afraid the ol' \K nightmare has come back to haunt us! mIRC crashes when a 'g' modified regex is supplied that matches an empty string and includes (?=___\K) to reset the start of the match to a position later in the subject:

Code:
//noop $regex(a, /(?=.\K)/g)


*kaboom*

"The only excuse for making a useless script is that one admires it intensely" - Oscar Wilde