The problem - when VirtualBox starts virtual machine, window has very
small height (couple of pixels) and it requires some manual fiddling
to resize it to something usable.
See related bugs here:
https://www.virtualbox.org/ticket/14718#comment:19 - small horizontal
line in the middle of the screen is newly opened virtual machine's
window.
https://www.virtualbox.org/ticket/15863
Inspecting with xdebug and xprop reveals that VirtualBox sends wrong hints:
Request(12): ConfigureWindow window=0x0660000a values={x=27 y=559
width=720 height=65512}
Which is interpreted by X server wrongly and shown with xprop as
WM_NORMAL_HINTS(WM_SIZE_HINTS)
:
user specified location: 27, 559
user specified size: 720 by -24
program specified minimum size: 254 by 109
window gravity: Static
Some part of X11 interprets such large value as signed int and wraps
it to negative value.
The solution will be if program requests such big window - detect it,
ignore requested size and resize it to some reasonable defaults.
Disclaimer - I tested it only on Ubuntu 16.04, but should apply to
another systems as well - see bug reports.
Gaspar Chilingarov