drop_index fails with OperationFailure if no index found on collection

Trying to drop a non-existing index results in the following:

command SON([('dropIndexes', u'MyCollection'), ('index', 'my_index')])failed: index not found

While the method description says:
"...Can be used on non-existant collections or collections with no indexes..."

should be handled by allowable_errors, exactly as in case of "ns not found"

Environment details:
> uname -a
Linux ... 2.6.32-220.el6.x86_64 #1 SMP Tue Dec 6 19:48:22 GMT 2011 x86_64 x86_64 x86_64 GNU/Linux
> mongo shell
MongoDB shell version: 2.4.8
> pip freeze | grep pymongo
pymongo==2.6.3