Unexpected behavior with local index provider and mixin properties

Using the new index feature of modeshape 4 we have detected some queries that do not behave like expected. Without the configured indices the queries work.

The following node types are defined:

[my:authored] mixin
- author (STRING) COPY
- coAuthors (STRING) multiple COPY
 
[my:content] > my:authored
- content (STRING) mandatory COPY

With the following query we'd like to retrieve all contents that are either authored or co-authored by the same person(s):

select * from [my:content] where author in ($author) or coAuthors in ($author)

But instead of the correct results we always get duplicates of the same node entries.