Confirmed--my iRiver H330
has the same symptom; when I press a button after the backlight turns off, the screen comes back but the play info seems to have frozen.
It's odd, but it seems like with conditional tags (same line displays current track and alternates with next track every three seconds), some information behaves correctly (next track displays and scrolls fine for three seconds) until it switches (current track does not display; next track simply freezes for three seconds, then resumes scrolling as usual).
I haven't tried it on a wide variety of WPSs, though.
I imagine they're working on it as best they can; as long as my music keeps playing, I'm fine with it.