I confirm this. Looks like the reason for having wrong kernel headers installed is the following dependencies chain: * virtualbox-ose-guest-x11 depends on virtualbox-guest-x11; * virtualbox-guest-x11 depends on virtualbox-guest-utils; * virtualbox-guest-utils recommends virtualbox-guest-dkms; * virtualbox-guest-dkms depends on dkms; * dkms recommends linux-headers-686-pae | linux-headers-amd64 | linux-headers-generic | linux-headers.
VirtualBox doesn't enable PAE/NX by default, so the installer chooses the 486 kernel for installation; however, when requesting virtualbox-ose-guest-x11 installation, no kernel headers package is explicitly requested by the installer, so APT chooses the default one, which is the first one in the dependencies list, namely linux-headers-686-pae. I guess, this can be fixed by explicitly requesting the kernel headers package, matching the kernel installed. -- Алексей Шилин
