OK let's clarify what you want:

You want a mIRC script that will respond to a peice of text with the format "somenick(id) - !blahtest" and check if that user (minus the (id) portion) is on the current IRC channel?

Code:
on *:TEXT:& - !blahtest:#:{
  var %nick = $gettok($1, 1, 40)
  if (%nick ison $chan) {
      something here
  }
}


That should work. If it doesn't then either there's another script interfering or there's something else going on you haven't mentioned.

Spelling mistakes, grammatical errors, and stupid comments are intentional.