So, I was bitten by the bug in v1.24 that screwed up my corners. Today I have literally just downloaded firmware v1.25 from GitHub and Ground Control v1.25.
I compiled and flashed the firmware to our Arduino and then started Ground Control.
Imagine my surprise when Ground Control threw up an error message saying there is a version number mismatch: GC v1.25, firmware v1.26.
Edit: never mind. Downloaded current repository, not v1.25 snapshot. D’oh!