Hmmm, and something else I just noticed. When the phone is locked, I can pause and skip ahead from the lock screen (but still with no album art). But when I pause it, then turn the phone off, then back on again (not restarting it, just the power button), the Poweramp controls disappear completely. I've been using Poweramp for a couple of years, and it's always stayed paused on the lock screen for as long as I left it there.
The artwork thing is an annoyance; this other thing is a major problem. I don't want to be unlocking my phone and hitting play again every time I have to pause it for a few seconds.