Sidebar problem

Strange problem on one page of my site
https://www.fleetwood-trawlers.info/index.php/2011/05/s-dt-ocean-lux-yh84/

The right sidebar has dropped to the bottom of the page. Other pages are unaffected so I don’t think it’s the theme.
I’ve deleted the page and re-created it and also disabled the plugins in case they were confusing things but nothing works.

Oddly though, the problem is there in Firefox and IE but not in Safari, which displays the page perfectly.

Any ideas would be very welcome.