Andreas,
Yes, there is an issue for sure. When I reduced the bytes per write(50 or less) it seemed to work better. I tried a range of file sizes, 1kb-~20kb, in my testing, it didn't seem to effect the results.
I didn't try writing, so no comment on that.
Thanks for the link, but still not sure of the process on updating. Do you use avrdude to compile and upload? Did you update the firmware and still have problems? If you did, I will wait to for the Arduino guys to update the firmware.
Thanks,
-diesel