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(details of which are not posted in this thread)
Not many details to report - it was just one of those "perl.exe has stopped working" type of messages as the program (ie any program that had loaded Gtk2-WebKit) was exiting.
I don't know the exact details of what was going wrong, but both libgcc_sis_452.dll and libgcc_s_dw2-1.dll (which were identical) had been loaded by different parts of the program. Restructuring so that libgcc_sis_452.dll was used throughout fixed the problem.
My guess is that, during exit of "the program", a handle was being thrown to the wrong dll.
NOTE: The 2 dlls were not actually identical, but were close enough to identical. I did replace libgcc_s_dw2-1.dll with a copy that *was* identical to libgcc_sis_452.dll and it made no difference.