In LaTeX, \llapand \rlap render their content in text mode. I found this while creating LaTeX screenshots as part of #268. The image has KaTeX to the left, LaTeX to the right, and a diff of both below.

The RlapBug test case also looks different in LaTeX: its numerator is centered. Is this a consequence of the mode change, in some way?

(With a bit of luck, fixing this issue will also get rid of the weird non-determinism of the Lap example when creating screenshots.)