nvidia-drivers and virtualbox-modules pull vanilla kernel

[dr_Fell]

Hello.
Today I am doing global update (to be honest, I didn't do it for some months). What surprised me, is that emerge is trying to install vanilla-sources. So, I checked if something changed - but no, still, gentoo-sources seem to be the default source for gentoo kernel.
So I checked, that vanilla is pulled by linux-sources-1, that one is pulled by nvidia-drivers-343.22-r2 and virtualbox-modules-4.3.18.
Can someone explain it to me? Why those packages need vanilla, while gentoo-sources was sufficient before?

[ct85711]

linux-sources is just a virtual, do you have a copy of gentoo-sources installed on your computer?