Why can't the Keyboard Shotcuts: Playback/Previous work, it works as the Keyboard Shotcuts: Playback/Stop? I only installed the component of Monkey's Audio Decoder 2.1.6.
The same for me but I'm not sure if playback/previous was working as previous any time before.
Is your playback order is set to "random"? In that case, previous behaves like stop. If you want randomness and be able to jump to the previous track, use playback order "shuffle (tracks)" instead. See foobar2000 FAQ on random VS shuffle playback order (http://www.foobar2000.org/FAQ#random_shuffle_playback_order) for more details.