They don't accept damma if they have alif maqsoora at the end, as in the word mustashfa meaning hospital, or alif as in zakariyya. Although the words can be grammatically marfoo, they don't take damma so you can't have mustashfu, zakariyyu etc. They will always remain mustashfa, zakariyya.
I will try to find how you describe their irab in the marfoo state, and post it here when I find it insha'Allah.