OK, Im having a think on this, but I need to refresh myself with
how my code works first, so give me time... maybe a couple of days...

Firstly, to try and remove the random "crash on exit issue",
try putting "on_esc=NULL;" at the beginning of main,
and re-enable my while(proc_status... line.
default.c has an on_esc function that almost-instant-closes.
I think it is making the code skip some (if not all) of the
port_close stages, thereby leaving the port open and crashing.

From memory, I have not (intentionally) limited the COM port numbers to 8,
but if I find something during my memory-refreshing process, I'll take it
out and let you know...