If the Name/Artist/Copyright data in the Export NSF dialog are changed, FT subtly behaves as if the corresponding fields in the main program have been changed to the new data (e.g. FT puts asterisk in title bar and the FTM, once saved, contains the new data), but does not update the fields in the main program with the new data.
Inserting/Removing/Deleting a frame by right-clicking it in the frame editor doesn't immediately update the "Frames" count in the "Song settings" box until one moves their mouse over said "Frames" count. This also applies when you do a [Edit>Clear patterns] on a module with multiple frames. Very similar to a past bug.
Strange things can happen if you're editing a song while it's playing (with follow mode disabled). E.g: When I type a note into a channel, sometimes FamiTracker will step to the next row (per edit settings) and other times it will not. Not sure why, need to test further.
