If you run the sample and make the window smaller, does it exhibit the same problem?
No, that's what I don't understand. Your demo doesn't exhibit the problem, but i cannot find any code in your demo which I haven't copied across. I know yours is filling up a window and mine is just sat inside a frame, but I can't see any of your code I have missed. I guess there must be something though.
i am just off to work but if you send me a picture of the screen i might be able to sus out a solution.
No problem, here's a screenshot of it.
As you can see the right hand edge of the dropdown is underneath the scrollbar.
If it helps, when I add all the properties, I call refresh to ensure that it has all the properties accounted for and then I call GetBestSize() and it gives me 60, 58 which is not remotely big enough for all the properties. I assume this is why it resizes too small when I add a sizer or even call Fit() on it. I'm not sure why this should be. It has lots of properties as you can see.