We run open mouth dogs. Based on my experience, I've seen them start quiet and eventually open - but never seen them start open and then go silent.
X2 on that, I got a cat/plott from Bosshog, she was silent until looking at a hog when I got her. She was like that the first 6 months I had her and huntin her with open plotts ruined her being silent. Now she is semiopen in hot sign.