The bug occurs only with vanilla saplings. For other modded saplings (like integrated dynamics saplings) it works correctly.

Argh 1.12 needs metadata, of course. I am sure that diorite will be placed as stone, too.
Actually for the diorite I should not fix it ;-)

It seems to work fine in the latest beta. I have tested only with stone variants and saplings, though.

Aye, I also tested with what was installed in my test setup. Let's close the issue for now, if we see something odd we'll re-open it.