The Palestinians make up the world's largest refugee group only because unlike any other refugee, their children inherit refugee status. That is something UNIQUE to Palestinians only. What this means in effect, is that second or third generation lebanese are labelled 'palestinian refugees' while they or their parents have never even stepped foot on the land.
Egypt to hold parliamentary election in 2 phases starting Oct 18-19 (Reuters)
from the article: As UNRWA turns 60, it asks for more funding for Palestinian refugees