I experimented around a bit and made my own thoughts about it.
It seems that each avatar has a cache memory associated with it, where information about the last operations (to undo) and from copying is stored. However, this cache memory seems to do a poor "garbage-cleaning", so that it overflows with large amounts of data.
As soon as a new room is loaded and the avatar is regularly brought back into the character editor, this cache memory is saved ... and is available again at the next entry. But apparently also with all the data garbage that has already accumulated.
If the room is left out of turn, no saving takes place and the working state is like at the beginning of the last entry.
Only when a new room is loaded and this new cache is saved, the data garbage from before is deleted.
This therefore occurs especially with rooms with larger memory requirements after longer working time.
Just my two cents to it, maybe I am wrong, but I really would like to know whats going wrong.