Did some digging around in the Inspector. See attached screen shots. The first is the good vs bad computed, which clearly shows the problem (highlighted). The second screen shot shows the only obvious difference I could find – there are two “Table” entries in the bad one, but only one in the good one. Both say User Agent Stylesheeet. The third is a full screen shot of the window.
The problem is only occurring when I go through the https->http proxy. Something is getting mistranslated? But this is the only window I have problems with.