safeCall blocks on large payloads

Hello wonderful people contributing to this project :)

I'm writing a distributed compiler using the client/server abstraction and ran into an issue with calls to safeCall (or other versions of call) not showing up on the server side.

Here is a reduced version (literally made by slicing down the existing project) capable of reproducing the issue: https://github.com/davnils/kool/tree/testcase
The pinned down dependencies are based on version in this post: https://groups.google.com/forum/#!topic/parallel-haskell/x3y6XNpTEFw

Basically there are executions of the client that end up stalling on call, which seems to occur with greater frequencies for larger payloads. I have reproduced the failing test case on osx but seen similar behaviour on ubuntu.

Any ideas on what could be wrong? Would appreciate any pointers or ideas on debugging the internals.