It's a Beryl Bug, that has not been resolved so far.
Many Java based application (Zend Studio f.e.) show this behaviour.
However just start the installer like this:
Code:
AWT_TOOLKIT=MToolkit sh zdesktop_linux_x86_0_36.sh
Could so add this to the bug report and resolve it as INVALID as it is not a Zimbra specific bug after all!