[racket] Possible bug in http://docs.racket-lang.org/more/step2.txt

On Ubuntu 11.04 (natty) AMD64 using Racket v5.1.

Saving http://docs.racket-lang.org/more/step2.txt as serve.rkt and
opening a Racket REPL in same dir. Execute:

> (enter! "serve.rkt")
> (define stop (serve 8081))

In new terminal run:

ab -n 1000 -c 8 http://localhost:8081/

This will execute 999 requests and timeout on the last 9 out of 10
times. -c 8 appears magical as -c 7 appears to execute with no
problems. Values higher than -c 8 also hangs.

Completely new to Racket so this is probably just me but behavior appears odd.