This is not a problem.
I just wondered if others have found items just appearing in the inventory. At first I thought these were things I had picked up, unnoticed, while excavating or using the time machine, but they definately are not. My current sim has picked up 7 items, a statue, 2 plants and the rest picturers in the last few sim days and she has not excavated anything or been time travelling.
For some time now, travelling with a bookcase in the inventory has resulted in multiple copies of book appearing in the bookcase, but, this is recent and happening frequently and randomly both at home and while travelling.