It's not lack of patience in my case. I've threaded each nut on and off at least three times with finger strength before even touching a wrench to try and make sure they were threaded on accurately. Plenty of grease.

Either I'm tightening the nuts more than I think I am (certainly no tighter than I tighten normal 15 mm axle nuts, and I'm only tightening them as much as I dare in order to keep the wheel from slipping), the axle threads are slightly damaged or (most likely) the nuts I'm using are alread too old to be trusted. The hub came with two nuts plus the barrel that goes on the drive side (it's separate from the actual drive-side nut, in this case) and all three nuts that I've had so far have been well used enough to have the edges rounded off.

Maybe I just need to find some better nuts. I'll see if I can find some one-piece drive side nuts for it.