Have you ever forgot to set the database when you ran a query, filling the master system database with your user objects? And I'll bet you used the dbo user too, didn't you? Doh!
Here's a quick way to ferret those out so you can clean them up:
/* Find foreign objects in the master database
Buck Woody - 2007 (with thanks to Jaco Schalkwijk)
Note: help_text is a Microsoft Object even though it returns
with this script.
WHERE OBJECTPROPERTY([object_id], 'IsMSShipped') = 0;
-- SQL 2000:
WHERE OBJECTPROPERTY([id], 'IsMSShipped') = 0