My info is based on dealings back. In 2010, things may have changed in that time, although I don't think the ruling on portability has.
I had a protracted fight with CL over portability, although I had been o/s for about 6 years prior to applying for OAP and was told I had to stay 2 years to keep the pension I maintained that my time o/s had been temporary as I was flying in as and out a few times each year. The reason I fought it was exactly what we are discussing now, I was told very clearly that if I departed anytime within 2 years my pension would stop, this didn't suit what I wanted so fought the system and was after a lengthy review by a seperate arbitrator classified as a resident and the 2 year wait period was waived - Lucky me.
At the time I believed I would need to virtually re-apply when I returned, that point I didn't chase up as I was pushing to be classified as a resident.