I noticed two times where we saw Morey Amsterdam laugh out of character:

-in S2:E10 "The Secret life of Buddy and Sally": he laughs when he pulls the telephone out of his coat and says "hello?"

-in S5:E2 "I Do Not Choose to Run": he laughs when he tells Sally "I'm agin it." She doesn't react and he immediately gets back into character.

He is always cracking jokes and smiling as Buddy, but these two times Morey seemed amused as well.

Were there others?

I can't think of any others, but I always especially enjoy "I'm agin it." It's natural and sincere and funny. Jerry Seinfeld did it a few times on his show by smiling slightly after a very intense moment and some people were annoyed by that. Again I thought he just couldn't help it and it didn't bother me.

Recently I've noticed Rose hiding her giggling behind her hands two or three times and I didn't get the same feeling. Because I couldn't tell if she was doing it in character as Sally, which would be okay, or if she was faking a giggling reaction as herself. Either way it didn't work as well as Morey's real giggling.