I noticed that the 42.3 repo actually builds against 42.2:Update.

I suppose this will make the kmps (virtualbox in particular) uninstallable on 42.3...

I don't see that in project config, where do you see this?

Hm, it was definitely there when I wrote the comment.

I had a look because the virtualbox kmps for 42.3 were only available for kernel 4.4.74 although 42.3 has 4.4.76 already...

Apparently somebody fixed it already though.