iTunes Bunching Artists in Shuffle


I am the woolrus
This is a problem i've had for a few a couple of months now and i can't find a solution to it anywhere!

If i put my itunes on shuffle, whether in all music or in a playlist, itunes tends to bunch groups of songs by the same artist together. I'll get 4 random songs played by one artist, then it'll switch to another and play maybe 6 random songs from them.

I don't know why it started doing this as before it used to shuffle properly. Has anyone else had this problem?