[racket] Getting unusual behavior from racket/sandbox: not truly capping memory usage?!

Hi everyone,

My hosting provider has been telling me that my compiler server for
Whalesong has been using about 1.4GB memory, but I'm _really_ confused
because I've got the whole thing under a racket/sandbox constrained at
256MB.  Perhaps I'm doing something wrong?


Here's what the sysadmins are telling me:

User - Memory - Elapsed Time - Pid - Command:
--------------------------------------------
dyoo - 102MB - 0:01:03 - 7519 -
/home/dyoo/local/racket-5.3.3/bin/racket sandboxed-server.rkt --port
16669
dyoo - 1446MB - 0:01:03 - 29032 -
/home/dyoo/local/racket-5.3.3/bin/racket sandboxed-server.rkt --port
16669


and my sandboxed-server.rkt is:

    https://github.com/dyoo/whalesong/blob/repl/whalesong/repl-prototype/sandboxed-server.rkt


where I thought I was very careful in ensuring everything important
runs under the sandboxing context, including web-server.  Am I missing
something obvious?