[code]...[/code] paragraph formatting is ignored on some pages, but works on others

Hi
(Sorry, this is a re-post of same question because, being a newbie to this forum, I didn’t know how to wrap the code snippets so you could see them. Hopefully it’ll work this time)

A mysterious thing has started happening on our site.

On some pages the html

...

paragraph tags are being ignored, on others they are working correctly.

For example ( on http://www.12steps.nz/clutterers-anonymous/ ) – text that consists of several

...

paragraphs is being shown as one block of text. e.g. under the title “About Clutterers Anonymous”

However, on a similar page the

...

paragraph tags are working correctly.
For example here – http://www.12steps.nz/emotions-anonymous/

I’ve tried changing the theme (e.g. to Aviator) but the problem persists.

URL: http://www.12steps.nz/12-step-programs/clutterers-anonymous/

URL: http://www.12steps.nz/clutterers-anonymous/