Sat wrote an article that highlights the difference between these types of events:

there are cases where it is much more convenient to circumvent mIRC's detection of $input in a 'critical' event (and it is actually possible to do so in mIRC script) but this isn't one of those cases :P using a split second timer to call an alias containing the appropriate segment of code is easy here.

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