But there are two issues, the BUFFER_SMALL was on one server and the
*zon error on the other. And it explicitely said that the data size was
5 instead of the expected 4, so this indicates that there is really
someting broken in that index.
I would suggest to combine your and Mark's proposal: remove the
substring index and reindex the database
Thanks to all who replied. I'm going to reindex the database tonight.