Light House Bug:

if you place a litte house with normaly wood walls and a slab´s as Housetop and you close it up with the last wall, you became a verry old Light Bug(see Picture 1), If you replace the top with normaly blocks or with double slabs you dont became this Bug(see Picture 2). I´m realy sure you already know this Bug and the Update History tells me every Update it give Light Bug fixxes, but never change this little tiny Bug.

Slab Bug

Another old Bug is the Slab Bug. If you place a single Slab in the World and place a different Slab(wayne if the Slab Wood or Stone) The second Slab is floating over the other(See Picture 3), but if you place the same Slab over this first you became a double Slab Block. I think it´s a tiny little Bug, because nobody has this combination build.