YMap Event "oldValue" is empty for yjs datatypes

I was wondering why the change.oldValue property of YMap (and maybe other yjs types as well) is emtpy if the oldValue would be a yjs datatype as well. It seems to me that in this case it is not possible to find out the oldValue somehow. Even an observeDeep does not reveal any further information.
I have build a small codesandbox to visualize what I mean.

Is this intended? Is it somehow possible to know what element got deleted?