Greetings!
Using Geany 1.37 on macOS 1.14.6 (Mojave) Intel there is a problem with the default theme. When selecting text in the editor then right-clicking on this selected text, often the right-click menu will appear then disappear, and then an Undo has been performed. So far it appears to be random but frequent enough to cause problems and frustration.
As a workaround, I had to quit Geany, go into the `Resources`->`etc` folder in the app bundle and rename the `gtk-3.0` folder to `gtk-3.0~`. After restarting Geany, a slightly different theme is in use and the right-click menu behavior is now working properly.
It appears that the excessive animation of the Geany-bundled default theme is causing the problem. After renaming the `etc`->`gtk-3.0` folder, the GTK-macOS default theme seems to handle the right-click and menu navigation correctly.
Thanks!