Somebody has made the rather arbitary (and hardcoded, boo) decision that the filename should be truncated to 30 bytes, but the path should be unlimited. Geany has no way of knowing how long to make the window titlebar AFAIK since it depends on window size and what decorations the WM uses, but sensible improvements in the current situation will probably be accepted.
In the meantime, there is a right click dropdown, but with 360 files its probably not much use.
There is also the document tab on the sidebar which is more useful for large numbers of files.