Yeah, it does seem like it should automatically try a different [random] port when a range/multiple-ports are supplied. The idea of port ranges is/was supposed to load balance users and to keep people/firewalls/ISPs guessing if some ports are blocked.

Would not expect mIRC to get hung up on a singular port, or attempt the first port necessarily in a portA-portZ range.

Well. At least I won lunch.
Good philosophy, see good in bad, I like!