Commander_X's 'quick fix' posted above appears to have done the trick!
Thanks so much to C_X and a_c for helping me out with this
Now I'm free to mangle the source code to suit my peculiar tastes
Redspear, have you changed user access privileges at any point recently? Check the shortcut used for msys.bat (right click, Properties, Advanced...). Is it set to run as administrator? You can try toggling this option and see if it helps.
That was certainly a possibility but no, I can run it as a regular 'user'. Thanks for investigating.
I haven't built it yet but I'll post back at some stage to (hopefully
) confirm a success!