Existing code for ungrouping did not correctly handle user counters: - counter for the group was not decremented - counters for containing nodes were not incremented The latter resulted in losing some nodes after orphan cleaning or several save/reload cycles. The bug did not have destructive consequences until recently, because it was compensated by another bug (fixed in rBe993667a46c2). Maniphest Tasks: T74665, T74682 Differential Revision: https://developer.blender.org/D7332