While a song is playing just pressing Previous Track restarts that track for me. If it's been less than a couple of seconds (2 or 3 maybe) pressing Previous Track skips backwards to the track before the currently playing track. But, if it's been at least 4 or 5 seconds of play time in the current track, pressing Previous Track definitely just restarts the current track.
There's an option that you might have set differently than I do:
Tools > Options > General > Behavior > Previous Button
I have it set to "CD Player Style".
Good luck.
Brian.