Invisible ToT spawns

[srmalloy]

The four doors on the west side of the central building in Kallisti Wharf (the center island, facing the statue of Statesman), when knocked on in the Halloween event and getting a 'Trick', spawn completely invisible mobs -- they can be targeted, and show information in the targeting window, but the mob model and the above-head name, HP bar, and End bar are all missing:

 

 

The mob in the screenshot above is a Crone, so this is not a case of a Spirit going immaterial and running away. This happens with all four of the doors on that side of the building.