DestroyWnd is called when the control needs to replace its window. For example, changing properties that are implemented by window parameter settings require the control to be destroyed and then recreated using the CreateWnd method.  

Before the window is destroyed, DestroyWnd saves a copy of the control's text in memory, frees any device contexts, and finally calls DestroyWindowHandle. When the window is recreated, the stored copy of the control's text is assigned to the new window. 

DestroyWindowHandle 

RecreateWnd