quirky language behaviour

[istilah]

Zencart 1.56c
PHP 7.3
Ceon URi Mapping 5.0, SBA and lots of modifications.

Let me take you to the backend, page is whosonline.
I am using 3 languages.

Not a big problem, but unpleasant unexpected behaviour: The admin page whosonline (backend) autoswitches language according to selected visitor (frontend).

Example: backend is on language 1.
When selecting/clicking visitors you can see their baskets
I click on a visitor who is using the site with language 2. (I can tell by the name of the visited page.)
When selecting a next visitor, my admin languages switches to language 2 automatically.

If this next visitor is visiting my site on language 3, my admin will switch to language 3 also when I select another visitor.

I do not have any modifications on this page, so I suspect the source of the problem to be a setting or plugin. But I haven't got a clue where and how to go about solving this.
Logs are empty.

Can anybody give me some clues?

[DrByte]

I believe the overhaul of whos-online in 1.5.7 fixes that.

[istilah]

Ok, i will copy that page over from 1.5.7 and see what happens.
I have to plan the complete update of that version later this year.
Thanks for your input!