Even Lords make brown paper bag mistakes. This is a left over code from my
initial testing, where the buffer where set with pre existing values to make
sure they were going through.  I forgot to remove them. As a result reads were
fine, but writes would just wipe the previous data from the buffer.
Incidentally, the "write-then-read-the-data-back" test I was doing would also
obviously pass, so I haven't noticed this so far.

Fix is to just leave the buffer alone.