🚀 go-pugleaf

I've been asked to try and get a rather large and extensively modified
Turbo Pascal (DOS) program running properly.  It's been locking up
completely when the program is exited, BUT by doing one of the following
I can get it to exit happily:

1. run xtree gold before the program is run
2. don't process the system registry on bootup (F8 on startup then
choose step-by-step and N to process the reg).

Doing either of these enables the program to run and exited reliably
until the PC is next rebooted.  I can also

3. set BootGUI=0 in msdos.sys so PC boots into DOS

To confuse things further, there are 3 slightly different versions of
the program, one of which exited OK without any of the above mods, but
now locks up with the BootGUI=0 setting, while the other two are now OK.

Any hints as to what I should look for in the program, methods or tools
for debugging.  It's quite a large app, with some 114 files, ISR's etc.

thanks (hopefully)

Hamish