Does desire have ext3 support built in? Can you try with the experimental 1.8.2.0?
I don't think the desire has built in ext3 support, but apps2sd is working fine for me. Anyhoo, I'm doing a 1.8.2.0 backup now, I'll let you know how it goes in a min (although I should point out that ROM manager claims I've got 1.8.2.0 yet when I reboot into it, it still shows up as 1.8.1.9, not sure if that's right or not?)