…or don’t detach your content db.
In server farms that have a large number of sites, installing a software update with the content databases attached can result in too much downtime. To minimize downtime, Microsoft recommends that you perform the additional step of detaching the content databases.
But this time, don’t do that for the last August cumulative update.
More details here http://blogs.technet.com/stefan_gossner/
The problem is being investigated