Shuffle is not random

When I click the "shuffle play" button in the web interface, the tracks that come up are fairly clearly not random. I've got maybe 90,000 tracks in my library from close to 6,000 albums and here's the kind of thing I get when I hit "shuffle play":

The same albums come up in a way that defies all probability.
Is there something wrong with my setup or is there something wrong with the way shuffle play randomises?

The same albums come up in a way that defies all probability.
Is there something wrong with my setup or is there something wrong with the way shuffle play randomises?