Perhaps I wasn’t that clear. I found the above define whilst trying to solve my own problem, but badly written theme or plugin is not the reason (I say not the reason, in as far as my investigations to-date, never say never)
The problem started when the site was upgraded up to latest version of all plugins / wordpress.
The problem disappeared when all plugins were disabled.
By enabling plugins 1 by 1 I identified that widget_logic enabled meant the wheelspun.
The theme is twenty ten, with no custom functions.php.
Latest versions of CF7 & Widget logic WP 3.8.1
I created a completely new install of 3.8.1 and added CF7 and Widget logic, and I could not recreate the issue in that new environment.
Its is not something I’ll likely be able to get to the bottom of quickly, as I will have to clone the live site into a test and start dissecting that piece by piece.
But with all plugins apart form CF7 & WL on the live site has a problem so eliminates bad plugin code. And Twenty Ten eliminates bad theme code.
SO that leaves me with content, which is a possibility, as there are afew text widgets, but I can’t dissect them in live.