Here is an interesting one I believe it's to do with that SEO plugin (Automatically parse links in text) by the looks of things...
Let's assume I type in the following:
Outside of a code block for example: src="http://www.sitepoint.com/forums/images/picture.jpg"
In some instances it inserts:
Infront of the text, which of course is wrong.
This is where I first noticed it happening: http://www.sitepoint.com/forums/graphics-8/graphics-wont-show-749890.html when I typed: src="http://www.sitepoint.com/forums/images/picture%20001.jpg" it prefixed the SPF URL.
Obviously I edited it back out and unchecked the check-boxes to prevent it reoccurring in that post. I know how to prevent that happening but nevertheless it still occasionally happens.
EDIT: it has occurred in this post too; I just typed the SRC for that QUOTE block NOT the SPF URL part!