Hi,
Yes it is a standard SAP functionality. When the stock is moved out of the SU managed storage location - either for the stock transfer or sales, then the SU from the putaway TO would be gone. It represents that the SU for putaway is no longer visible in the warehouse and you can't even see that in LS33.
However, if you want to retain that SU, then it calls for custom development. Even after that, you can only see the SU in TO and not is LS33.
Regards,
Sushant