So I discovered these bugs lately...
Looks like the () around the if statement makes it execute the command after ) if it's true
//noop $iif((1 isnum) echo -ag fail,1)
fail /!return 1
Your $iif() has a bad syntax. $iif((1 isnum), echo -ag fail,echo 1)
Also why do you need to noop it? I don't understand.
And.. mIRC has troubles parsing:
//echo -a $replace(ab.,},}) . c
I am not sure if its a bug or not, } is kinda a reserved character. But replacing it from a text using replace w/o $eval() kinda should return such results.