I suspect you are running into problems with the special nature of the $near query. $near performs both a limit() and a sort() on the cursor returning the results -
Specifies a point for which a geospatial query returns the closest documents first. The query sorts the documents from nearest to farthest.
By default, queries that use a 2d index return a limit of 100 documents; however you may use limit() to change the number of results.
http://docs.mongodb.org/manual/reference/operator/query/near/
While the documentation does specifically discuss overriding the limit of 100 with your own limit call
You can further limit the number of results using cursor.limit().
It is silent on adding your own sort() or both sorting and overriding the limit at the same time. I suspect you are running into side effects of doing both. Note that it's not incorrect to do both - it just may not produce the results you are looking for. I'd suggest trying the same query using $geoWithin
http://docs.mongodb.org/manual/reference/operator/query/geoWithin/
$geoWithin does not apply a sort or a limit on the results, so it gives you something of a more raw result set.