My only take away and the only one I can think of, giving the lack of any explanation by the writers would be.
The zombie Mountain does not think or feel. His only passion is killing.
He listened to the one that made him Qyburn & Cersei, who was the one his maker told him to protect.
But seeing his baby brother again (a true connection to himself) must of brought some feelings back into him, & also tempted his rage. The young brother that he loved to torture as kids. So that would’ve probably been the only time he disobeyed, because of who it was. If the Mountain had lived through that fight. I’m guessing he wouldn’t of disobeyed again.
Oh man, when the Mountain went to squash Sandor's eyes, it was like Oberyn Martell and the Mountain's speciality move all over again. I really felt for Sandor then, and I hoped he would finish off his brother definitively.
Same here, man. I was like, oh no not his eyes!? Have to admit, out of all the odd character arcs that make zero sense this season. Sandor aka The Hound was always good.
Hats off to Rory McCann!
He was always badass, cold & at the same time warm & caring. At least with Arya. A+ work. Great actor & hope to see him in many future roles.