Enabling editor causes error on links with "&"

Steps to reproduce:

• Edit a content object in the admin interface, such as an article;
• Click the "Disable editor" button;
• Type <link href="http://google.com/?this=that&something=nothing">link</link> in the textarea
• Click the "Enable editor" button;
• The following error is generated:

The draft could not be stored.

Required data is either missing or is invalid:
Body: Wrong opening tag