Shocking behaviour! I have found that buggy's are often an issue especially on smaller planes. Sometimes I am allowed and sometimes not - if not, I also try to explain that it fits and has done the trip - but, if I see it's not happening, I just let it go (albeit with a grumpy look on my face).
I did have an experience once a few years ago in Berlin with a 2-piece pushchair, not small - checked in - no tags were placed on the pram (I just assumed they would gate check it as I hadn't been through there before with a pram).
When we came to board the lady at the desk literally started shouting at me that I had "hidden" the pram and "lied" to her. I was stunned and told her that it was with me at check-in with a child in it right in front of her - and, she could gate check it there.
She told me that all the staff who could gate check it had gone home and continued berating me. Ended up boarding (they put the wheels section behind the captain in the cockpit), the ground supervisor came on board to my seat and lectured me. Was not very happy.
Since then, have gone with it and found the vast majority of crews to be extremely helpful.