Captions Problem

I run two sites and both appear to have the same problem after upgrading to the latest version of wp.

I use the visual editor and add captions to pages there. When I add captions, it puts a grey box around the photo and adds the caption text below the photo.

Suddenly (it seems to have happened after upgrading to the latest core with both my wp sites) the grey box doesn’t appear and the caption text appears unformatted below the picture.

I’m rubbish at HTML – but have noticed that the new html looks like this:

[moderator note: please mark any code using the ‘code’ button or by wrapping it into backticks – http://codex.wordpress.org/Forum_Welcome#Posting_Code ]

‘[caption id="attachment_682" align="aligncenter" width="420"]<img class=” wp-image-682 ” style=”border: 2px solid black;” title=”agv gp tech crash helmet rossi five continents” src=”http://billyscrashhelmets.co.uk/wp-content/uploads/2012/07/agv-gp-tech-crash-helmet-rossi-5-continents.jpg&#8221; alt=”gv gp tech crash helmet” width=”420″ height=”420″ /> The AGV GP-Tech in Rossi 5 Continents colours[/caption]‘

but comparing it to pictures that posted correctly, with captions, i’ve taken to manually adding the caption=” ” so it now looks like this (and this seems to work):

‘[caption id="attachment_682" align="aligncenter" width="420" caption=" "]<img class=” wp-image-682 ” style=”border: 2px solid black;” title=”agv gp tech crash helmet rossi five continents” src=”http://billyscrashhelmets.co.uk/wp-content/uploads/2012/07/agv-gp-tech-crash-helmet-rossi-5-continents.jpg&#8221; alt=”gv gp tech crash helmet” width=”420″ height=”420″ /> The AGV GP-Tech in Rossi 5 Continents colours[/caption]‘

However, if i make any changes using the visual editor, it reverts all captions back to the previous, wrong version.

Anyone know if it’s WP that’s broken? Or is there any way I can get it back working as before, so I can caption using the visual editor?

Thanks!