T17 map bosses dropping T13 maps with 4 voidstones

Second t17 in a row where the map boss has dropped a t13 map when I have 4 voidstones slotted in. Using corruption/escalation/monstrous lineage/multitude scarabs. Been running this setup for a long time in t16s, decided to run some t17s for challenges and noticed this. Shouldn't be possible as far as I'm aware, right? The map dropped in a loot pile from the boss itself.

https://imgur.com/a/cfnTqrb