Lava Chamber Map/Mirage

The mirage portal spawned in the boss arena in Lava Chamber in maps. I cleared the normal arena, then clicked on the portal.

I didn't start moving right away, probably a second or two, then when I started moving the mirage completion popup *instantly* triggered.

The cache was on one of the hot grids which are disabled in the mirage version of this map (does the ground effect even hurt monsters?), but I hadn't begun attacking anything at all - so something else killed the chain guys.

No other monsters seemed affected, other than the chain goobers apparently suiciding, it was entirely typical for the rest of the clear.