SQL Server Mirror failover on failing storage
Just to move my part into an Answer.
It would appear the "problem" is that the script in the blog ( http://sqlserverperformance.wordpress.com/2012/03/27/sql-server-database-mirroring-tips-and-tricks-part-3/ ) is using an ALTER DATABASE dbname SET PARTNER FAILOVER; to failover the rest of the 'failover' group. 

As all the dbs were on the same disk, this fails as SQL SERVER can't run the ALTER DATABASE command if it can't get in to the database. So moving the databases onto seperate disks fixes that.

But that sort of makes sense. If all the databases are on the same disk then they should failover automatically as a 'group' as they all need to be fail overed. The referenced script would make sense if you did have databases on seperate disks that needed to failover together if just one of the disks failed.