Mirroring Multiple Databases On A Single Instance

Can someone explain what does this mean? This is from http://www.microsoft.com/technet/prodtechnol/sql/2005/dbmirror.mspx



<quote>However, all these techniques for coordinating client redirection with a database mirroring have an important limitation. Database mirroring occurs only at the database level, not the server level. Be careful if your application relies on querying several databases on a server, or uses multi-part object names to query across several databases. When several databases reside on one server, and they are mirrored to a standby server, it is possible that one of several databases might fail over to the standby but the others remain on the original server. In that case, you might need one connection per database that you are querying, so that you do not attempt cross-database queries on a standby server where only one database is a principal and the remaining are mirrors.</quote>

Also I read somewhere that if one mirrored DB fails, all other mirrored DB should also be transferred to the mirror.

For example: Let's say Srv1 (principle) and Srv2 (mirror) and Srv3(witness) are SQL servers with only default instances. The SQL instance has 4 DBs (DB1, DB2, DB3, DB4) and all of them are mirrored to Srv2.

An ASP.NET application has four seperate connection strings like:
objConn1 --> Data Source=Srv1;Failover Partner=Srv2;Initial Catalog=DB1;Integrated Security=True;
objConn1.connect();

objConn2 --> Data Source=Srv1;Failover Partner=Srv2;Initial Catalog=DB2;Integrated Security=True;
objConn2.connect();

objConn3 --> Data Source=Srv1;Failover Partner=Srv2;Initial Catalog=DB3;Integrated Security=True;
objConn3.connect();

objConn4 --> Data Source=Srv1;Failover Partner=Srv2;Initial Catalog=DB4;Integrated Security=True;
objConn4.connect();

If DB2 failsover to Srv2 (mirror), why should all other DBs be failedover?

Thanks