Thanks MrFen.
I cannot say specifically why C C V however the admin has set up a pattern replace of some character sequences. This was during an especially heavy SPAM period lasting several months. There were some patterns in the posted URLs common to the spam posts and very rarely seen in genuine posts. As such, since we were unable to keep on top of the spam at that time the best (not ideal, but best) solution was replace certain patterns and neutralise a lot of SPAM. Unfortunately, this does result in the odd false positive but on the whole the balance is still in favour of the automated neutering.
I'm not certain if the pattern replace uses regex - if it does then we should be able to make it better targeted I suppose.