Pressing down doesn't do it, but a full reseat does. Still not sure as to why that is though.

Has to be said, on a sidenote, i'm quite liking this Slot Load drive in the Pismo... may have to mod up a faceplate for it. In the mean time, still need to find a Lombard/Pismo optical drive, CD or DVD, doesn't matter it just needs to be compatible.