Highlighted Terms is not NULL when searching a numeric range query

[Barba Papa <ba...@yahoo.com>]

I stored numbers as numeric and search them like this: "fieldName:[20 to 30]".
I expect highlighted terms to be Null, but in some ranges it is null and in some other ranges it is meaningless characters. 


It seems that depends how many search result is found, different 
types of query is generated in "rewrite" function in 
"ConstanScoreAutoRewrite" class. If few result was found it generates 
BooleanQuery and if more results is found it calls 
"MultiTermQuery.CONSTANT_SCORE_FILTER_REWRITE.rewite()".
When BooleanQuery is generate highlighted Terms are not Null.Why?
I am using Lucene 4.0.0.