[U of M Sam]

My take is simple: Be very clear if you verbalize a call such as "safe" or "no catch" during the situation described. "No catch" could sound like "catch" when verbalized along with all the noise of the game. I tend to say "NO" when a ball is not caught during a play as you mention.
Coaches will sometimes try to shift their lack or responsibility or situation knowledge toward the umpire, which I think is "goofy". The runners have a responsibility to know the situation and adjust accordingly. When I played high school baseball, I was always taught to run until you hear "foul" or even "out" depending on the situation.