When there is an interrupt signal that should be handled during get/set in implscope functions that can fail, they don't pass up the interrupt. They instead pass up that they were forced to exit with their own errors, and the interrupt signal is lost. During the mr_killop test, this results in the test hanging – the mr operation is not killed, but the test is still waiting for an acknowledgement. This only happens when there is at least one function in db.system.js.