I couldn't reproduce this. Tried sending the /url -a while IE7 was open, and also closing it between each try. Everything in mIRC stayed as I would expect. Is it just that command you're trying, or is something else happening when you call it?

I used:
Code:
//var %input = test | tokenize 32 %input | url -a http://www.google.co.uk/search?q= $+ $1

from the command line

Sais