Hi again,
while I'm following the other thread of this discussion,
something came to my mind:
The usb storage code in the kernel has several sub-options
which, when activated, integrate some special "support
code fragments" into the driver, namely for a few Flash
Reader products... and although the HP isn't explicitly
listed there, and as you're downloading the kernel source
anyway (you used a precompiled image before, I presume?),
it might be worth a try activating them all and compiling
your own kernel, just to eliminate possible problem sources.
:)
Jan