Full screen tool bar does not work properly on Linux hosts

[FiveYellowMice]

In full screen, the bottom tool bar does not appear as quick as it does before 5.1 when mouse approaches bottom of screen, and no hover effects when mouse hovering on the buttons.

When click a button on the tool bar for the first time, it will work as usual. However, after that, these buttons become decorations. The virtual machine is normal, but the only ways to quit it is to either let itself power off, or use shortcut to minimize all windows.