Eldritch altar re-appears after boss defeat & entering Vaal side area (#2,360,652,594)

While I'd heard of other display bugs involving the new Eldritch entities, this was a bit new: I encountered an altar for the Eater of Worlds, and clicked a button and began the encounter as normal.

...However, after killing the map boss, (and clearing a Vaal side area) I swept back to this area and found that the altar & hits buttons had re-appeared! Both buttons did nothing, though visually & audibly reacted to clicking. (they just failed to make the pop-up disappear)

While I did leave the zone to enter a Vaal side area (clearing it) I have not left the map entirely; this situation appeared while there are 5 unused portals in my hideout.

Bug Report #: 2,360,652,594.

Reproduction: Not reliably reproducible; most important factors seem to be that I selected an option that affected the map boss, then killed the map boss, then entered a Vaal side area.

Screenshot: attached is a screenshot of the altar having returned.