If you run a server (from the open to LAN option) using one login, and then use a different login to run the server. The inventory from the first login is copied, and the inventory from the second login is lost.
MC-17785
Server login inventory copy
Resolved
Duplicate
0
There are at least a half dozen bug reports on this issue, going back at least to v1.4.6. All of them have been marked "Duplicate" except MC-5405, which has been marked "Invalid". The net result is that the moderators keep saying this is a non-issue, when in fact this continues to be a debilitating issue years after it was initially reported. The bug prohibits multiple players from playing on a single computer. It is open and it needs to be fixed.