I guess its working as expected, I see different Labels on your screenshot (C,D,E) and hence it is treating them as separate drive's, there are 2 ways to resolve this:
1. Do a list resource on the node uncheck everything on list resource and submit the same. Wait for one polling cycle check from node view if old drives disappear. If they disappear do a list resource again and add the new one's. If point 1 does not work go to point 2
2. Directly remove old drives from DB, Drives are present under Table "Volumes", keep the nodeid handy.
Open Node View -> http://solarwinds/Orion/Net/NodeDetails.aspx?NetObject=N:XXXX
Use the below query to list the drives on DB:
SELECT * FROM Volumes where NodeID=XXXX
And then remove the same from DB
Hope it helps