Yes I found that they could get out but always had more probs getting back in.
I didnt think Sasa could use it at all but found that when I blocked it up to try and keep her and misa in at night, she broke out and ran away, then found she could get in too when she came back.
She does have more problems than the others cos her little legs are shorted abd cos she usues her nose to pushe it, so if wing is blowing against the flap it takes her a few goes to get out.
I find that all cats have their own way of getting in and out too, Sasa pushes corner of flap with nose, Misa pushes with paw followed by head, Ducha pushes a paw through and levers it up and Franta just pushes with head I think.
Forgot to say that Kocka used to sit inside and bang with paw, so I would hear flap.........flap flap ........and if I didnt go and open it for her to walk through by then , it would be come ,,,,,,,,,,,,,,,flap flap flap flap flap flap
To get back she would climb up on the window sill and tap the window.....tap, tap tap and if that didnt work she would bring her claws down the window which was like chalk squealing on a blackboard. When I went out she would look at me all angelically and climb on my shoulder to be carried in, in the manner she thought she deserved
When I wasnt there she would come and go all by herself