Since the comparator will always be LT or LTE, retval.lookupType has always been set to one of these, here. 
It is not possible that retval.lookupType == IndexLookupType.EQ.
It seems like there should be additional conditions on resetting retval.lookupType -- it should not be reset if an ascending sort direction has been established.
The reverse scan optimization is probably not advantageous enough to make up for an extra ORDER BY node.
I think this is what Xin was suggesting in his comment on the test case.