Since a couple of days (no kde updates that I remember), I have a random but not very frequent problem with a small (two buttons) panel set to autohide.
The panel is on the top left of the screen. Sometimes happens that the panel do not show when I move the cursor to its position but if I slowly move the pointer along the top edge of the screen, when I'm more than half the distance from the other edge the panel flash for a moment on its position: after that, the panel acts normally again.
Also, if when the problem happens I restart the session, the panel returns to normality.
No idea what triggers the behaviour. This can happens at the session beginning or after a while: there is no visible pattern.
openSUSE 11.4 64 bits with KDE SC 4.6.3.

Cheers

So I discovered that the position of this tiny panel depends on the windows I have on the desktop: if a window (for example, a dolphin instance) is on the top left corner of the desktop and I move the cursor to the position on which the panel was created, the panel flash for a moment to the right of the window and then I need to move the mouse pointer there to see the panel. I then I close or move the window, I need to put the pointer on the last position used by the panel: then the panel flash on its right position and then I can use it normally... up to when a window goes there and everything starts again.
I ended by moving the buttons to a "windows can cover" panel and deleting the autohide panel.

I have setup a panel on my KDE Trunk system to test this, but as of yet have not been able to reproduce the problem. This could be related to a corner case bug perhaps, or alternately a damaged configuration.

Thanks. I'll try again after upgrading to 4.6.4 and come back to report.

Edit: It's working now under 4.6.4