We recently upgraded to 2.13 and noticed that some of our problems were not rendering (a pg compilation error was reported) when the "Render All" button was clicked in the problem set detail page. Those same problems displayed fine in the library browser or when viewed individually.
After further investigation, we found that the problems with this issue were in DOS/Windows format (crlf) and converting them to UNIX format solved the problem. I'm not sure why the difference, but thought it might be helpful to mention in case others experience the same challenge.
Walla Walla University