While this is a bug, it's not with mIRC, but rather Windows, as the numbers that you're dealing with are so large they exceed the maximum calculation for a number using a 32 bit base (which is what Windows 95 - XP use.. NB: Excepting Windows XP Pro 64)
The largest number that works on 32 bit OS (which is what you're using) is equal to 2^56
This is, fairly obviously, going to be a smaller number than the 10^50 level that you used as your start point.
btw: 2^56 = 72,057,594,037,927,936
Seventy-two quadrillion fifty-seven trillion five hundred and ninety-four billion thirty-seven million nine hundred and twenty-seven thousand nine hundred and thirty-six.
For 64 bit OS's the number would be a lot larger, however, I don't have access to a system running a 64 bit OS at this time in order to figure it out.
