Again, for posterity, and in case anyone starts to dig into resize soon:
Bug 913245 - resize2fs w/ large block & inode count is going badly
https://bugzilla.redhat.com/show_bug.cgi?id=913245
Contains a fair bit of weirdness, but the outright problematic bug is that it's allowing the number of inodes to grow past 2^32. Loopback reproducer is in the bug.
The fs ends up quite corrupt, as well, and seems to not be growing by the correct amount, etc.
Seems like resize needs a lot of love still.
-Eric