Ian: I don't know enough about the BinaryResponseWriter or shard searching to really know what the root cause of the problen is here, but it sound like a bug that should be fixed ... could you pelase file one in Jira and mark it "Fix Version: 1.3" (we should figure it out before 1.3 goes out)
my only guess is that this is a BinaryResponseWriter variant of SOLR-424, where the ResponseWriter isn't being forgiving enough of an empty string making it into the index for a numeric field (but you probably want to try and debug how that empty string got into that field ... that's bad) -Hoss
