Trouble adding a tag

Hi all,

This is a weird one (I think).

Basically, I want to add a tag to all my previous blog posts. The tag is ‘little black dress’. However, WordPress won’t let me add it. Every time I try to update a post after adding the tag, the tag just disappears from the tags panel. I’ve tried adding it under ‘post tags’ too, but with the same outcome.

All other tags seem to add just fine – it’s only ‘little black dress’ that’s giving me grief. Does anyone have any idea why this might be?

I thought it might have something to do with the fact that I’ve added tags before reading ‘SOMETHING [eg. Chanel] little black dress’ – so that when I type ‘little black dress’ into the ‘add tags’ field now, WP suggests a bunch of existing tags containing the phrase. But I’m not sure if this is at the root of the problem or not…

Any help would be MUCH appreciated!

Thanks!