updating docs when using SortedSetDocValuesFacetFields

[Rose, Stuart J]

I'm using Lucene 4.4 with SortedSetDocValuesFacetFields and would like to add 
and/or remove CategoryPaths for certain documents in the index.

Basically, as additional sets of docs are added, the CategoryPaths for some of 
the previously indexed documents need to changed.

My current testing with using writer.updateDocument(docIdTerm, docFields) seems 
to be generating some duplicates as there are more documents in the index than 
expected.

Is this a known issue with SortedSetDocValuesFacetFields and discouraged?

Thanks!
Stuart