Running the following code on 2.6 rc0:

db.bug.ensureIndex({'isactive': 1}, {name: 'find_active'});
db.bug.ensureIndex({'IsActive': 1}, {name: 'find_active'});

Results in the bug collection with an index for:

{'isactive': 1}

NOT an index for

{'IsActive': 1}

My expectation is the second index would either replace or co-exist with the first. It is not that the first index is kept and the second statement is ignored.