Version:            (using Devel)
Installed from:    Compiled sources

My setup is nvidia twinview with two monitors side by side running KDE 4.00.80 (KDE 4.0.80 >= (KDE 4.1 Beta1) on kubuntu.

My use case:
Start KDE4
Right-click on right monitor to create a new panel. It appears at the top of the right monitor as expected.
Click the cashew.
Try the drag panel to the right and bottom edges of the right monitor. Nothing happens for me.
Drag it to the left edge of the right monitor. This works (but leaves some corruption at the top of the right monitor after the move).
After this, dragging the panel anywhere on the right monitor does nothing. It won't even go back to the top again.
If we try to drag the panel onto the left monitor, it starts to behave the way we'd expect if we were dragging it on the right monitor i.e. moving it to the bottom of the left monitor actually moves it to the bottom of the right monitor. This works for the top/right/bottom edges but not the left edge (but we can get the panel to this edge by dragging to the left of the right monitor as it should work).
Also, if I drag from slowly from left-to-right near the bottom 80% of the left monitor, the panel quickly switches between being on the bottom and right edges of the right monitor.