I'm running 1201 - this has only just started happening recently, no scripts installed, using the skinned version. If using the non-skinned version, then the tracks appear fine, im not running a different or modified theme, or colour scheme, am running Aero though (if that makes a difference?).
Nothing appears in the list panel (although things do appear in the Now Playing window)
In the bottom left, MM does list tracks, its just they're not visible.
Doing a CTRL + A and then pressing enter does make them play.
Running Vista Ultimate.
Mike.