New fields added when saving field group

On some field groups by error new fields appear when saving the field group. All these fields have the Name of other fields in the same group but don’t have a label. They are all of type Text.

I don’t see any pattern which fields could trigger this behavier, the names are taken from different field types like Message, Post Object or Date Picker. After disabling ACF qTranslate this behavior can’t be reproduced any more.

Any hints why this could happen?