That happens on mine all the time. I don't have 13k songs on it but I have hundreds.

I suspect it's a problem of most randomizing algorithms not using truly random numbers. I've run into this problem in doing programming a few times.

I wrote a quote generator for a website I had years ago. It uses php to pull a random quote from a database. But quite often, out of over 500+ you'd get the same one twice or more in a row.