killThread hangs on GHC 7.0.4 7.2.1 but NOT 6.12.3 and 7.4.1 about distributed-process HOT 2 CLOSED

#!/bin/bash

set -e

function go() {
  VER=$1
  make clean
  GHC=ghc-$1 make DemoTransport.exe
  mv -f DemoTransport.exe DemoTransport_$VER.exe
}

go 6.12.3
go 7.0.4
go 7.2.1
go 7.4.1

Fix #4988: we were wrongly running exception handlers in the
maskUninterruptible state instead of ordinary mask, due to a
misinterpretation of the way the TSO_INTERRUPTIBLE flag works.

Remarkably this must have been broken for quite some time.  Indeed we
even had a test that demonstrated the wrong behaviour (conc015a) but
presumably I didn't look hard enough at the output to notice that it
was wrong.