Strange culling behavior - Foliage

Okay okay, it’s definitely the grass mesh, but I do not know why, to be honest. I created a new map (in the same project) and placed some grass patches. The same problem - I replaced the mesh with one of my crate mesh and it works perfectly. Now I have to get a clue what is wrong here ^^

I will be back soon with more information.

EDIT: For me, this is a bug.
In case it isn’t, please explain me this behavior:

First screenshot. I’ve painted some grass with the fresh imported grass.
Culling doesn’t work (well, it works, but with the described problems).

Second screenshot. I switched the mesh. Culling works as expected.

Third screenshot. I switched back and et voila … it works for some time. After tabbing onto the desktop and back it’s broken like before. It’s wonderful _