Waited for a week and hadn't heard back from Marantz Pro so I gave them another call. Talked to a different rep and he informed me that a file had been started on my issue and they were going to try and recreate the problem to see if it's my individual deck or the ones they have as well.
Next day I get a call from the first rep I spoke to and he told me their decks did the same thing and " that's how this deck works - if it loses power it will not save the file in progress ".
There are a couple of things that don't add up - I was 80+ minutes into a 4 channel recording when the deck lost power so where did the info - the 2 ~1.5Gb stereo wavs that had been written to the card go?
Other decks have a file with an incomplete header if this happens (including other Marantz decks) and you can recover the file by writing a new header - I've done it just by opening the file in CD Wave Editor and saving as direct wav which affixes a fresh header to the file and off you go.
The rep claimed that nothing had been written to the card since the file wasn't saved properly - that doesn't jive - when you stop a recording on the 706 a window appears that says "SAVING" for maybe 2 seconds then the deck returns to the record screen and is ready to start a new file. It's physically impossible for the deck to write the whole file to the card in a 2 second burst when you stop recording. That info is on that card! Support just can't explain where or how to recover it.
I got an email from the support department after my ticket had been opened so I will pursue the idea that this is a big problem for end users who operate in the field and face power disruptions regularly. I left a review on the B and H site where I bought the thing letting prospective buyers know about the bug.
Hopefully they will actually do something about it.
I plan to continue to use it because to be honest I like everything about it - except that my NYE headliner show went up in smoke - I'll just find a more robust probably right angle USB plug and will keep a better eye on the battery indicator from now on...