The supervisor tests seem to fail intermittently. This is almost certainly because the tests rely on ordering guarantees that the CH doesn't really offer - viz ordering between multiple producers and 1 test case process, or ordering of monitor notifications - yet we should try to do something about this.
It seems easier to provoke failures by running with +RTS -N1
t4@iske:distributed-process-platform $ ghc-env active
t4@iske:distributed-process-platform $ ghc-env env
Active Site: no active sites
Active Compiler: 7.6.2-x86_64
t4@iske:distributed-process-platform $ uname -a
Darwin iske.local 11.4.2 Darwin Kernel Version 11.4.2: Thu Aug 23 16:25:48 PDT 2012; root:xnu-1699.32.7~1/RELEASE_X86_64 x86_64