Hard max length for latex code in markdown cells?

There seems to be a max limit to the number of characters I can input in my latex-markdown cell. The code below compiles fine. If I, however, try to add a new line with more than 21 characters, it doesn't compile (see the bottom of the "not working"-file.

I am sorry for the horrible code I am posting below, but I was unable to reproduce it in a clean way and was forced to just anonymize the real code and replace it with this silly-looking latex code.

[latex in markdown - working.txt](https://github.com/jupyter/notebook/files/3409672/SO.-.working.txt)
[latex in markdown - not working.txt](https://github.com/jupyter/notebook/files/3409671/SO.-.not.working.txt)

Start by comparing the attached “SO. - working.txt” and “SO. - not working.txt” files, focusing on the added line that exceeds 21 characters. Trace how LaTeX in markdown cells is processed and identify where the limit appears. Done means the reproduced longer line compiles without changing valid existing behavior.

Written by the indexing model from the issue text.