Question regarding re-attaching databases

We tried to backup a database for RMS by going through Management Studio, d etaching the database, copying out the mdf and ldf files and reattaching. P
roblem is, whenever we tries to reattach, no matter what name he gives the database, and no matter what computer he tries, it says that the database a lready exists.
If you query the sys.databases table, the database we try to attach won't b e there, but then after getting the error that the db already exists, it wi ll mysteriously appear in the sys.databases table. It will even say that th e database exists on brand new installs of SQL.
I have a feeling that there's an issue with the master dbs but I can't say I've ever seen this problem before so I'm not sure exactly how to fix it. A ny ideas?
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