Views Admin Ajax screwed up

Hi - I'm posting here and not in Views forum as I suspect this is more an ajax than a Views issue...

I must've altered something to my site to make this happen (it used to work fine) but I've no idea what or where... Any guidence in either direction would be gratefully received.

When I go into Views admin and open a View then edit something using the Ajax console and then when I go to "update" the display (the step before a save, it comes back with something like the following and I lose my change;

{ "replace": { "#views-tab-default": "\x3cdiv class=\"clear-block views-display views-display-default\"\x3e\n \x3cdiv class=\"top\"\x3e\n \x3cdiv class=\"inside\"\x3e\n \x3cspan class=\"display-title\"\x3e\n Defaults \x3c/span ...... etc etc

If I view source it shows the above text is wrapped with <.pre> and <./pre> tags

I don't know anything about Ajax so I'm not sure if they're supposed to be there or not (or how they might have got there if they're not supposed to be there)

I'm a bit stuck till I get this sorted out - thanks in advance for any guidance

Duncan