Both my AMD-based and Pentium-based PCs don't crash with Online's example. But do crash with more than 2 DCCs.
Here is another test script I propose, this is the same as Online's, but this one increments by one dcc window each time. It starts at 1, then 2 (which exactly matches Online's script), then 3... until mIRC crashes.

Code:
alias dccbug {
  if ($1 !isnum) { set %magicnumber 1 }
  titlebar Now testing with %magicnumber DCCs
  var %i = 1
  while (%i <= %magicnumber) { dcc chat 127.0.0.1:1 | inc %i }
}

On *:close:=:window -c =$nick | if ($window(=127.0.0.1, 0) == 0) { inc %magicnumber | .timer -m 1 500 dccbug %magicnumber }


This would be interesting from the "non-crashing PCs" out there to test this one, to see if they *really* don't crash, or if they just need more dcc windows to crash...