autostarted mintwelcome.py shows nothing on boot

[npaqq]

version: linux mint 13 maya
edition: Xfce 64bit

I've booted Linux Mint 13 Maya Xfce 64bit edition on VirtualBox from ISO image.
After installation of the edition to a disk (vdi file) and reboot, usually mintwelcome
screen is automatically shown on top of a screen and it shows a template html.
But in this bug case, mintwelcome is running but it shows only white rectangular
box and user cannot close the window.

It is difficult to reproduce, but this bag is found frequently on the first graphical
boot (with X11) after installation. somtime it found 2nd or 3rd boot or directly
starting mintwelcome from a terminal or from mint menu.