Yes it is strange.
I have a lot of sets I'm trying to sell. I was just checking out the feature to see if I wanted to use it. I find some had the buttons and others did not. As I get time I will be adding more and hope they all will have the buttons.
Have not find a real reason why I'm seeing what I seen.
Side note: How does members know the sets are for sale?
Just did 1993 Topps Baseball. I had several cards for sale but none in my collection. I pulled up the set and did collection summary and NO buttons. Added one card to my collection Then I went back in and sure enough there was the buttons. STRANGE