In his statement at the 2014 IAEA General Conference, U.S. Secretary of Energy said that the United States "just completed another shipment of HEU from Poland in cooperation with our Russian counterparts, making Poland one step closer to being HEU free."
Although no details of the shipment are available at the moment, the material in question is most certainly the spent fuel of the Maria research reactor. The reactor used 36% HEU fuel supplied by Russia, but it was converted to LEU in 2012. Some spent fuel containing HEU was removed in September 2012 and in 2010 (there were shipments of fresh fuel as well - in 2012, in August 2007, and August 2006). The removal of spent HEU fuel is expected to be completed in 2017.
Although the reactor has been converted to LEU fuel, it is producing medical isotopes with HEU targets. The material for targets is supplied by the United States.
UPDATE: The fuel was delivered to Russia by a cargo ship Mikhail Dudin operated by Atomflot. On September 29, 2014 Atomflot reported that all fuel has been transferred from the ship to railroad cars to be transported to the reprocessing plant.