microSD data corruption

In trying to get an FSO-daily on my microSD card, I discovered some microSD corruption: I copied a 35MB file over USB via scp straight to the micro SD card... and it was bogus. So I copied it instead to /tmp, which is on a ramdisk - and it worked fine. So to verify, I then tried to copy the file from /tmp to the micro SD card via 'cp'... and it was again bogus. So there's some corruption hiding there. This is with qtopia 4.3.2 rootfs and kernel.