Unexpected culling strikes

Greetings!

I may have miscalculated something, but have noticed that I almost constanlty "Culling" rare monsters. Yet none of similliar mechanics were taking in build.

Not all rare monsters. But about half of them. And unfortunatly I can't trace reasons or conditions.

If you need any information from me, pls let me know.

After some tests.

It seems somehow related to freeze or stun. Because non of act bosses or really tough rares are not "culling".

Upd. It does seems work like Mace Mastery. Yet I didnt take it on passive tree.