Mr Revellbikes
I wonder if we are twin souls.
Today was one of those days when a baby bird decides to parachute down the chimney of my wood burner. They take turns at this, and I have developed a routine to free them whereby I throw open the windows and patio doors before I open the wood burner door and watch them hurl their little sooty bodies at any window that I have left shut. They seem to particularly like the velux on the opposite side of the room from the fire. It had been stuck for ages, but I thought a little determination with the hook would fix that. It did open the window, but it also split the vent flap away from the metal fixing in just the way that you describe. And my internet trawl found your comment which so accurately described the design and the obvious issues with it.
did you get any joy from Velux? I have cobbled my window back together so that it is properly shut, but I will not be able to open it with my pole and hook unless I replace the whole flap. This is not a serious issue for me, but may be for the fun loving birds playing games in my chimney.