I will address the issues in the order you entered them:
1) The wrong height for the maximized window is a known issue under IE9 and it has been fixed in the latest release (Q1 2011 SP2).
2) When the RadWindow is minimized only its titlebar should be visible.Trying to open it again without closing it first is not a correct scenario as the opener code would try to set the required size, while the CSS class for the minimized window is still applied and allows for a smaller size, which will result in a conflict.
4) The OpenerElementID property should be used in simple scenarios and is not absolutely guaranteed to work in INaming containers, with AJAX callbacks and/or when some other custom logic can overwrite the handlers or dispose the objects (the RadWindow and/or the opener element)
"OpenWidnow(); return false;"
//custom logic here
All the best,
the Telerik team