I haven't been able to do the Facebook sharing ones at all. I tried various different achievements & medals. Like you said, I am able to share normal achievements/completed games all the time (an error sometimes, but usually works right after).
Haven't tried the other one. I got the one for beating a personal best and a few others by accident.
100% Retail: 21/68 ; 100% Arcade: 41/67
Most Recent: Clive Barker's Jericho / Scarygirl