Sounds to me like one of two things.
1) EK HR posting on prune to say there is such a policy to prevent loosing pilots.
2) Some other pilots with an interest in SQ trying to stop high time 777 Captains from applying ( therebye increasing their chances)
We'll see who is right. I know of a few that have moved either way , so that invalidates the alleged policy to date. Why on earth would competitors care about such a policy. Quite the opposite it would make sense to take your competitors pilots . Alas we will see.
As for the " internal source at SQ". Same rule applies. Perhaps an SQ guy who has it in his interest if SQ cannot find experienced people.
Now back to the origonal rumour. Are SQ hiring on the 777 , any news gents ?