Short update, it appears that values are saved to and read from the wrong language with 5.0.3 and before.
Have a fieldgroup in main language with field 1 and field 2. Added a translation of this fieldgroup in secondary language, with field 1 only.
Now saving values in field 1 works in both languages. But if I enter something in field 2 in main language it does not get saved, field 2 stays empty.
I think that’s because field 2 does not exist in translation of fieldgroup and so the value can’t be saved.
This problem usually won’t be noticed if main language and translation have same fields. Everything looks fine, but actually values are both saved to and read from wrong places.
This observation matches the above described behaviour with the not matching key in my log.
Edit: I don’t know why this topic is marked as solved, it is not.
