This was bedeviling me for awhile. I could not figure out why my RQLQueryRange droplet was not sorting by dates correctly. It turns out this is a known ATG bug which only happens when you are using Oracle, which is 99% of the time.
Considering that this bug has been open since 2003 one can assume ATG is not interested in fixing it. This is probably because there is a simple work around.
Instead of using the sortProperties parameter, put the the sort directive directly in the RQL statement in the queryRQL parameter.