so, my email from last weekend had gone unanswered, so I gave tech support a call.
the first guy basically told me that they haven't tested the 16 gig cards, and that they couldn't be guarenteed to work. I told him that "no, it didn't work, the unit froze on me. twice." and I made clear that the SanDisk Extreme III series of CF cards
is, in fact, on their list of approved media. I told him that I thought it was a quirk in the firmware, because in the "media information" screen, it shows that the card is 16391 MB, and the count down of remaining recording time is consistent with 16 gig of space, so the unit is clearly able to "see" the full 16 GB. it just locks up when it gets to 8. when I asked what the likelihood of them releasing a firmware update to fix this issue, he basically told me "maybe" and I should keep my eyes peeled on their website. great, thansk for the help...

so then I asked if he could transfer me to someone else. and he transferred me to his supervisor (I assume so, anyway, because the 2nd guy I spoke to was still in the tech support department, and told me during the conversation that he "wasn't an engineer"). So, this second guy, at first, was telling me that while he wasn't 100% sure of the reason, it is possible that the HD-P2 was only designed with 8GB in mind, and that it may have been a "design constraint" that the unit was built around. I then told him many reasons why I didn't think that was true i.e. "from a storage point of view, the 16 GB CF card is formatted as a FAT32 volume, which is the same as a 4 GB card or an 8 GB card" and that basically, it didn't make any sense that this issue would be because of a "design constraint". I repeated everything I told the first guy, and firmly told him that I believed that the issue was a quirk with the firmware, and that it was my impression that a firmware update could fairly easily resolve the issue. in the end, he took down all my information, and said that he'd pass it along to the engineers, and that I would be contacted by either him, or an engineer.
so, of course, I'll keep everyone updated with the latest info from Tascam. at this point, I've redid a test (my second test at 24/192, just to fill up the card as quick as possible. the first time it locked up on me, I had 5 or 6 Phish shows on there from DAT transfers, all at 16/48). so it's happened to me twice now.
edit to add: if anyone else runs into this problem, and wants to call Tascam, I can give you the name of the guy I spoke to (the 2nd guy). PM me for that info...