The way we solved this problem is that it turned out we had only a few hundred rows with unicode keys, so we simply extracted them, upgraded to 0.7, and wrote them back. However, this means that among the rows, there are a few hundred weird duplicate rows with identical keys.
Is this going to be a problem in the future? Is there a chance that the good duplicate is cleaned out in favour of the bad duplicate so that we suddnely lose those rows again? /Henrik Schröder