David,
The marc.include_errors is intended to malformed marc records, but it
doesn't enforce any repeatable/non-repeatable restrictions on the Marc
record. However I agree that crashing is not a good outcome for when a
record unexpectedly contains multiple versions of a field that should be
non-repeatable. If you e-mail me some of these bad records, and your
index.properties file (if it is different from the standard VuFind index
configuration) I will make the program much less crash-y when it tries
to put multiple pegs in a single hole.
-Bob Haschart