In reply to Matthias Pfefferle.

Didn't seem to be TinyMCE, so I'm not sure what could be causing the difference. Feel free to close this for now. I'll reopen if I see other edge cases or behavior which may be relevant.

For those interested in manually preventing the automatic hashtag behavior in some cases I'll note that adding things like a zero-width space ​ between the # and the tag text seems to be useful. I'm sure there are other similar methods...