Trac HTML previews for patches unavailable

One of the neatest features of Trac are rendered, colorized HTML previews for changesets and uploaded patches. But lately Trac is decreasingly able to show such previews for patches; instead it renders the “HTML preview not available. To view the file, download the file.” page. Only options then are to download the patch or view it as plain text.

Why is this happening?

Trac isn't the cleverest at deciding whether what it's got is a patch or not.

- Matt

My last foray into trac editing was a disaster, so i'm not too sure where to start. If anyone has trac experience and is keen to have a poke around i'll see about getting some kind of access sorted