I recall, it was Federal's use of a different primer compound, that was more likely to chain ignite...or maybe that was just a Lawyer thingy?....Is that why they excluded Federals? The boxes were too big to easily dump into the trays? To be honest I have used Federals continuously for years (SR's in .223/5.56's) with the old style round tray Lee priming tool without a single problem.
(I am looking for a piece of wood to knock on now that I opened my big mouth.)