This might be loosely related to an older question of mine.
I was answering a question at Mathoverflow and after posting I obtained a number of upvotes (in some sense signalling that everything was fine) until the OP complained about some “strange symbols” not rendering properly in his computer. It actually seemed OK on mine.
I edited the answer, nothing strange there until I copypasted the text onto Emacs and there I noticed some strange chars (labelled by a squared "OBJ"). So I corrected the post on my editor, pasted it and it was fine.
Added. I'm using Chromium browser version 48.0.2564.82 Ubuntu 14.04 (64-bit) running on
Linux XXXXXX 3.13.0-77-generic #121-Ubuntu SMP Wed Jan 20 10:50:42 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
uname -a). The only browser plugin installed and working is TeX for Gmail v.5.19.5.