mattparlane/mongo-php-driver — pull request #1 by hacklschorsch (2012-01-03 20:21:47+00:00)
Title: Please see my Unit test. 

Sparse indexes work for me with and without your additions (as do "dropDups", for example).

I modeled the unit test after http://www.mongodb.org/display/DOCS/Indexes#Indexes-SparseIndexes