it is not unusual that a pushed slide film gets a cast. I have never pushed RDPIII 2 stops, but had similar effects with other films. You can't blame the lab for that, because every film behaves different in the push-process (which is non-standard) and color adjustments can only be done with ph-changes of the CD-bath, which would affect all other films as well. Only self-processing gives you full control over the material you know.