How would a client with only Editing Mode NOT Design mode change the active tab to be able to edit the tab pane content for all tabs? I am unable to find this anywhere.
You should just be able to click the tab and edit, I’m not aware of any issues here however I’ve seen some changes to the editor lately and a few new bits of weirdness. There may be a bug here.
It may also depend on how you’ve setup your tabs, e.g. if your tab title portion completely fills the tab then clicking it could switch to edit mode on the text element rather than triggering a tab change. Can’t say, I’d have to dig into the setup to figure out what was happening.
For anything that looks like a bug, contacting support is your best bet.