virtualbox.org

Hi,

Host is debian 7 (64-bit)
Guests are debian 7 and ubuntu 10.04 (both 32-bit), debian 8 (64-bit)

Since guest additions 5.0.18 both older guest start without 3d acceleration.
Desktop start in gnome fallback mode only.
Manual install of guest additions 5.0.16 works around the issue.
I tried with 5.018, 5.0.20, 5.0.22, 5.0.24 and 5.0.26. Issue persists.

Debian 7 guest is gnome 3.4.2 and kernel 3.2.0-4-686-pae.
No custom repository, no backports, just standard install with up-to-date packages.

Debian 8 guest has no issue.

Probably the same thing I've been seeing with Ubuntu 15 and 16 VMs on a Windows host:
https://www.virtualbox.org/ticket/15526

That ticket is in a stalemate until somebody much more knowledgeable with Linux than me is able to provide more troubleshooting. My observations so far is that the problem involves incompatibility with the host, at least in my case, as affected VMs function properly with the latest guest additions and 3D acceleration on two out of three computers I have access to. And on the third computer, it only happens sometimes. I remote desktop into the third one often, so VirtualBox may be having problems with that in the way some other programs (like Firefox) don't properly handle changes in 3D capability of the display.