Apparently Lucene does not reliably raise an error if there is a mismatch between field type and requested sort type. E.g. see this case which returns wrongly sorted results for a field type of String and a requested sort type of Long.

The error you see I believe only pops up in some special cases (maybe involving an analzyed field?). Would be good to know the test which raises it. I saw it before but cannot remember how I produced it.