I experience some strange issue trying to use formulas in Codeforces blog post.

The steps to reproduce: go to your profile, press "Write new entry", place dollar sign character, then sh (two characters), then dollar sign character into content field (total four characters) and then press Preview button.

Expected behaviour: italized sh in preview.

Observed behaviour: Unable to parse markup [type=CF_TEX] message in preview.

What am I doing wrong and what to do about it? I tried to post an article containing many formulas and was not able to do it. I reduced it to the smallest test case. Several other two-letter combinations produce a strange result too.