Hello, Kaffeine v.2.0.5 from the debian/stretch repository can't minimize to the tray icon anymore. This was particularly useful during recordings or pure audio playback. Minimized means: it was no longer part of the taskbar, could only be reaccessed by clicking the kaffeine tray icon.
That was fixed on Kaffeine v2.0.6. Please take a look at BZ#370918. *** This bug has been marked as a duplicate of bug 370918 ***