The menu for "Add file(s) to bottom of playlist" is stuck in German and will sometime pop up on its own. System's language setting is English(US) and this is the only menu that's in German. The menu will sometimes pop if there's a few files in the playlist, but no files will appear. At least, I haven't noticed it when it's empty. If I open the menu normally, a second menu will appear on top of the glitched on and both ill disappear.
1.6.5 has a different problem that makes it unusable though. I'm going to see if it happens on more than one machine before submitting a bug report, but when I launch it on the one machine, the icon is the Syncplay icon while loading, then turns into VLC and VLC is what actually loads.