Hi changhai,
In further testing, I've been able to narrow down that the problem only exists when the virtual machine guest window is run on any other monitor bar the primary monitor.
My setup has four displays (three external, plus the laptop display). The primary display in this configuration is one of the external displays, and moving the vm guest to either the second, third, or fourth windows causes this issue to appear.
The menu bar auto hides and re-appears when the mouse hovers at the top of the display properly, when the vm guest is on the primary display.