Ok - yet more frustration.
After hours of trying (and failing) to make RT crash when running under gdb.exe, I reverted to running RT normally. I opened a raw file, and it crashed within probably less than a minute of opening the file. So short was the time-scale for this, that I remembered everything that I’d done with that image file.
I then opened RT under gdb.exe again, opened the same raw file, and carried out the same operations… it ran perfectly, with NO CRASH.
Any more suggestions?