Since upgrading to OpenCV 3.2 from 2.4.3 (I believe it was around that), a window created using OpenCV fails to display any graphics if minimised immediately after creation, even if it is brought back up. The standard white cross still appears in the window as the mouse is moved across it, but no graphics can be displayed. If the window is left alone after creation and the first graphics are drawn, all is well; the window can be minimised, graphics drawn etc. and the window brought back up without issue.
Not sure where/how to report this issue.