I now understand the problem. WP Survey and Quiz Tool loads a script file containing jQuery Tools (https://flowplayer.org/tools/). A comment in the file says
* jQuery Tools 1.2.5 - The missing UI library for the Web
*
* [tabs, tooltip, overlay, scrollable]
Theme My Login loads the jQuery UI tabs module, and this must conflict with the jQuery Tools version (see stackoverflow.com). Certainly if I rename the script file so it can’t load, the problem with Theme My Login goes away.
I’m not a Javascript expert, so I don’t fully understand how the conflict occurs and I can’t suggest a solution, but if I were jeff I’d want to see if there was any way I could protect my code from a conflict like this.