Okay - I finally sussed this one out. Just in case anyone else has the same problem:

Here's what causes it

You write a post and you incude URL links
You preview the post before submitting it
You go back to editing and the post has been changed to include html...this html is the links you included. Your message will have {url} and {/url} prepended and appended to all the links <- note I've had to change the square brackets to the curly ones or I'd be in the same boat again)


Here's how to solve it

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BB code is On
Smilies are On
[IMG] code is On
[VIDEO] code is On
HTML code is Off <--- this is the one

Cut your message and paste into notepad
Remove the {url} and {/url} <-- the real message will contain square brackets
Paste back into your message and submit.

Phew