Rich-Text toggle is missing and Fieldsets can't be opened/collapsed -- but only for users with Site Admin role and Zen theme

Issue Summary

It will be obvious from the following that I am pretty much a clueless newbie. I really have tried very hard to solve this one my own. I'm just not making any headway.

The following problems are occurring *only* for user with the role "Site Admin." Everything works fine for all other users.

It also only happens in the Zen 6.x-2.1 and Garland 6.22 themes and not in Chameleon 6.22 (but still just for Site Admin users).

Both problems go away if I switch the compression level at admin/settings/jquery_update from "Production (Minified)" to "Development (Uncompressed Code)."

1. The Rich-Text toggle is missing from all text areas that use Filtered text, and Rich-Text is disabled.
If it's relevant, I'm using WYSIWYG 6.x-2.4, and my editor is TinyMCE 3.4.4

2. Collapsed Fieldsets cannot be opened and Collapsible Fieldsets cannot be closed.
(The text labels are there, but they're not clickable and the little triangular arrow is missing.)

The default site theme is Zen, and Users who do not have the "Site Admin" role all see "Disable Rich-Text" underneath the text area and can open and collapse fieldsets in the Zen theme. So, to repeat, it only happens for Site Admin users.

This happens in Firefox, Safari and Chrome. (No easy IE access with which to test.)

The rich-text problem was first noticed a few minutes after I enabled JQuery_UI 6.x-1.x-dev and FullCalendar 6.x-1.4. When it was noticed, the rich-text problem happened across all enabled Themes (Zen, Garland, Chameleon), but when I disabled FullCalendar and JQuery_UI, it went away in Chameleon, but remains in Zen and Garland. The fieldset problem never manifested in Chameleon.

I assume that both were happening before in Zen and Garland as the Site Admin who first noticed it is the person who does the vast majority of our content creation, and she has selected Chameleon as the theme for her Site Admin account. So, while exacerbated by JQuery_UI and FullCalendar, it was probably not caused by them.

So, the good news is that my colleague can go back to creating content using Rich Text as long as she sicks with Chameleon, but the bad news is that I have to figure out how to fix the problem in Zen and Garland ... or remain indefinitely in "Development (Uncompressed Code)"

I've been reading lots of different related issues in the issues queue for other Modules, but I don't have *any* of those Modules installed/enabled. (For example, Lightbox and Better Select are the two mentioned at http://drupal.org/node/507240, but I don't use either of those.)

Thank you so much for your help.