Hi Steve,
My reply was only partly directed at you; I also tried to explain some general principles to the topicstarter. I forgot to say that the MCP speed window can be closed again, terminating the speed intervention, by pressing the IAS/MACH selector once more. This should bring you back to VNAV PTH, as long as automatic mode reversions don't interfere (so it's no use trying to do this when flying 3000 feet above a computed 250 kt descent path while flying 320 kt). Pressing VNAV again, as suggested above, should also work as VNAV PTH is the default VNAV mode (with the same caveats).
But (over)complicated it is! That NASA paper I mentioned stated: "The VNAV function (also known as the PROF function) accounts for the majority of reported human factor issues with cockpit automation". From an engineering point of view, the VNAV mode is probably very clever, but aircraft designers are no aircraft operators.