JimH: I _still_ believe this is a bug in MC. How many other reports are needed to accept the fact? All this reminds me of "Comical Ali" ("There are no American infidels in Bagdad. Never!") 
IMHO, one properly made report would help a lot. You would need to provide JRiver a way to reproduce the bug.
I can't reproduce it on my three different PCs (using the ASIO, Direct Sound, Wave Out or Disk Writer output modes.):
- a homemade desktop: MSI MB / P4 / Intel Chipset / XP home / integrated C-Media CMI9739A audio and Terratec DMX 6fire 24/96 soundcard
- a Fujitsu Siemens D-8820 laptop: P4 / SiS chipset / XP Home / integrated Realtek ALC202 AC97 audio
- a homemade desktop: Abit MB / AMD Athlon / VIA chipset / Win 2000 Pro / SoundBlaster 128 PCI soundcard
A proper report should include at least the following:
- complete system information (soundcard, chipsets, drivers etc).
- complete information about the used MC options.
- information about the last MC version that does not have the problem.
- a sample audio file (if the problem is dependent on the file format or size)