Hmmm, down in the Miscellaneous options there is something about links, let me take it off and see if it stops doing this for me too.
Yup, it worked. It the second Fyi
At least that what I think it is, I'm no expert
Miscellaneous Options
Show your signature
Automatically parse links in text
Automatically embed media (requires automatic parsing of links in text to be on).
Automatically retrieve titles from external links
Disable smilies in text