Horned Scarab of Pandemonium change bug?

Horned Scarab of Pandemonium no longer spawns bosses on maps as before

I'll add my findings to this.
It seems to work in most situations, but not all.

If I run it with ambush scarab of containment, it seems to only spawn the original map boss in the normal location, but it doesn't seem to spawn bosses on the map, or in the strongboxes. If I have an altar with the map boss dropping certain loot, I only see that loot popping up once when the main boss is killed, and I don't get many astrolabes (one in every 5-10 maps, instead of averaging 1--2 per map.

If pandemonium is run without containments, then it works fine.