Thanks for bring it up, I'd been meaning to post an update. It only does it right near my house, it seems to be a low power station based at the local high school, or something of the sort. I've tried turning AF and TA on and off, any they seem to have no effect what so ever. I remember this was an issue when 2.0 was still in development, but don't remember the details.
Ah, I should have consulted the FAQ:
Why did the tuner change stations on me?
(Entry last updated on January 21st, 2005)
This might be caused by a bug in the RDS-AF (Radio Data Service Alternate Frequency) feature in the 2.0 final software.
RDS-AF is supposed to switch to a stronger station as you move between different areas. But it only works in Europe, because that feature isn't used by radio stations in the USA. It seems that the software still tries to do some of that behavior even when the data signal it's getting is random garbage. Unfortunately, turning off the AF feature on the player's main menu seems to have no effect.
If, when listening to a specific radio station, your tuner seems to occasionally change to another frequency, try rolling back to player firmware version 2.0 Beta 13. It's been reported that this fixes the bug.
But why hasn't it been this way for the last five years? My tuner's AM reception dies occasionally, I wonder if the whole thing's on its way out.