Version: (using Devel) Installed from: Compiled sources - set panel to auto-hide - click its cashew - drag its height button upwards the containment is suddenly truncated, leaving only about a quarter or less of the desktop at the top. the rest is the root window.
This should be a duplicate of #176280
Marking as duplicate. Please reopen if the auto-hide part was indeed relevant. *** This bug has been marked as a duplicate of bug 176280 ***