Hmmm, lets see
| Scintilla | GTK | Result | --- | --- | --- | | 3.6.3 | 2.24.30 | Ok | | 3.6.0 | 3.16.7 | Ok | | 3.7.5 | 3.22.26 | bad | | 4.0.0 | 3.22.30 | Ok |
IIRC there were a number of problems with GTK 3.22 and Scintilla, maybe you are hitting one of those which has been fixed since 3.7.5. Any chance you can try a later Geany (its up to 1.35 now with Scintilla 3.10.2), maybe from the [PPA](https://launchpad.net/~geany-dev/+archive/ubuntu/ppa) if you can't build yourself.