I have the exact same problem, but doesn't have the events calendar plugin installed...
When publishing an article, I get a bunch of "s in the source code, replacing the image url.
When inserting an image into a post, I get the following code:
<a href="http://odin-media.net/marius/wp3test/wp-content/uploads/2010/08/pp-logo.jpg"><img class="alignleft size-full wp-image-11" title="pp-logo" src="http://odin-media.net/marius/wp3test/wp-content/uploads/2010/08/pp-logo.jpg" alt="" width="200" height="287" /></a>
but then I press the "publish"-button, and by magic, the HTML output is
<a href=\"http://odin-media.net/marius/wp3test/wp-content/uploads/2010/08/pp-logo.jpg\"><img class=\"alignleft size-full wp-image-11\" title=\"pp-logo\" src=\"http://odin-media.net/marius/wp3test/wp-content/uploads/2010/08/pp-logo.jpg\" alt=\"\" width=\"200\" height=\"287\" /></a>
Please note that this is when having HTML-view activated. If I go to VISUAL-view, and press the "publish" (or now "update")-button, the HTML output for the image is
<a href="\"><img class="\"\\"alignleft\"" title="\"\\"pp-logo\\"\"" src="\" alt="\"\\"\\"\"" width="\"\\"200\\"\"" height="\"\\"287\\"\"" /></a>
Does anyone have an idea on where I can fix this? I assume there is a function printing or converting the URLs that must be fixed? any help is much appreciated!