Table with Sortable Columns Possible Cacheing Issue

This problem is baffling me (although I baffle easily).

I've got a view with a page display that uses the table style (view export attached).

I develop in Chrome so everything tested fine. When I asked the client to look at the copy on a development server they noticed that in FireFox if they clicked on certain column titles it didn't appear to sort. I tried it in FireFox 3.6 and sure enough it didn't sort as I expected. So I tried it in Internet Explorer 9 (and using IE's developer IE7 mode), it failed there too.

I searched the issue queue and thought my problem might be related to #339107: Table with sortable header not highlighting default sort column, #772620: Pager dissappears when sorting date field by DESC, or #1133738: Sorting by Node: Post Date ASC fails to display all results, but DESC works fine., but none of them had solutions that appeared like they addressed my problem.

So I switched to Garland, following the issue requirements. The view almost worked. Generally the sorting did what I would have expected. So I figured it was a theme related problem. The theme is a "hacked" version of Zen, unfortunately whomever created the theme just modified the zen directory so I can't switch to an unmodified version (easily).

But the really strange behavior appeared after I switched back from Garland to the custom theme. When the sort failed, it also switched to a Garland rendering. So I figured "clear caches," which I did (even the views caches). Problem still appears, although on occasion it will switch to a display that is the custom theme but without the custom page template that loads if all goes well. The display in question is at http://friends.vt-host.info/staff-directory.

Like I said it only appears in FireFox and Internet Explorer and not Chrome. And if I simply reload the page it appears to switch to the correct display.

It's obviously some kind of odd cacheing behavior, either at the browser or inside Drupal, but I cannot for the life of me figure out where the problem is.

Any pointers? Thanks in advance for any help.