Yeah… I did some troubleshooting in the original topic (Renaming caused file deletion bug.) and reproducing it wasn’t a problem – understanding why it happened was a problem. 
I failed to understand it, partially because I didn’t have the know-how (or possibly energy) to deploy full scale debugging tools on Android. IIRC it didn’t reproduce on my emulator, only on a physical device, which is more locked down.
It also happened when renaming between dash and underscore, which Syncthing doesn’t consider equivalent under any circumstances. This made me suspect something external, since even if our case-rename-handling is entirely screwed up, it shouldn’t take effect when renaming things like that.