AddTerm disabled in SDL Trados Studio 2019 SR2 for non Multiterm glossaries?

I use a different TerminologyProvider than Multiterm and since updating to Studio 2019 SR2 adding terms to my glossaries is no longer possible via my ITerminologyProviderViewerWinFormsUI implemetation.

Neither the shortcut nor the options on the ribbon or in the context menu work (the latter being disabled/greyed out).

From what I can tell AddTerm/AddAndEditTerm won't be triggered any more (breakpoints won't be hit) unless a Multiterm glossary ("termbase") is added as the default provider. Of course all terms then go into that termbase instead of my glossaries.

Can anyone confirm?

Is this a bug in SR2 or by design (to discourage the use of alternative terminology sources)?