Strangest cannot resolve symbol error ever

This is a not so uncommon error:
But when I switched to PooledHttpClient.java I got a bit confused:

Seriously w t f happened here? Has my RAID controller gone berserk on the poor file?

A couple of weeks ago I saw something similary happend on a production server (VPS).
Suddenly one of my static HTML-files contained fragments of code from something completely different.
As far as I can tell, these errors seems to originate from a broken file system.
Perhaps one should take stuff like this as a sign that it might be wise to start replacing the disks in the raid array.