Strange glitch: "Displaying nilclasses 1 - 15"

While looking at the “changeling” tag, the first page of results behaved strangely. Instead of “displaying images”, it said “displaying nilclasses”, and it only displayed 13 images instead of 15. I checked several other tags, and they didn’t return the same error; however, searching for “changeling” and “changeling, -queen chrysalis” did. The second and further pages displayed normally; only the first page of results glitched out.
 
For reference, my filter was set to “All Images”.
 
I think something strange is happening with two specific images. Any idea what it could be?