Press "search" twice in tuner mode. The first time brings up the "enter a frequency" dialog, the second used to crash the player or make it sluggish and stop responding to certain commands.

That's in the internal bug list... twice.

Also, there is a seemingly-related bug on the internal bug list: Entering out-of-range frequencies into that tuner dialog (for example entering 1610 when it's on FM). Produces a similar behavior in the player.