I don't know about it being broken as I've never had my Sim automatically go to meet up with another unless it was a specific event or opportunity driven like with World Adventures.
In my game, when a Townie phones my Sims to hang out and I accept the offer, my Sim doesn't automatically head out to meet them, I have to send them. However, the Sim who called has been known to wait for my Sim to get there and they do indeed hang out (actually, autonomously spending time together).
Other times, I'll agree to have them 'hang out' and the Townie Sim will call back to say something has come up, they can't get together at that time (which I personally think is thoughtfully cool). When that happens, I track the Townie down to see what came up and every time (so far) something has indeed happened which called them away.