Did you set your retention low enough in the SnapManager Configuration utility?
One note here, but from what I understand SnapManager for SQL Server is on the way out and they are using either CommVaults snapshot solution or something else rebranded. I don't have all the details but some of the issues may go away with those changes. We'll see....
David
@SQLTentmaker“He is no fool who gives what he cannot keep to gain that which he cannot lose” - Jim Elliot