Do you have the AutoScaleMode set to DPI?
...
Thanks for pointing this out, once I read it, I was sure it was the problem. Kean wrote about it
here.
Took me a while to find it, turns out it's on the background of the control, not the controls themselves. Unfortunately, the change made it worse. I'm wondering if it's related to the way the palettes are coded. I've noticed that AutoCad doesn't do well in general with DPI scaling on hi-res screens.
Looks like I'll stick to a manual adjustment of 1px down for now, thought it feels like a kludge fix.