cannot add translation to set

Using the latest localizer 5.x-3 modules, I'm creating a new node, I invoke the translation tab and I create a new translation for that new. Afterwards, I disconnect/detach the translation from the set again. So far everything works fine. If I now select the detached translation from the dropdown menu and try to add it to the set again, I'm getting the message:

translation successfully added to this set.

However, to me it seems like this translation was not added to the set yet. I'm aware of the fact that the version 5.3 of the localizer module is still in an alpha stage, so my question is whether this function has been implemented already?. Or is this a bug? I encountered the same behaviour both on MySQL and PostgreSQL based installations and can't find any errors in the server logs.
Thanks for your answer
Andreas