The main reason I had to rollback to using Qt 4.8.5 since I was developing on Qt 4.8.7 on a Windows 7 machine was because after upgrading to Windows 10, my 4.8.7 apps failed in so many levels. Something as simple as loading an image was completely broken. I did a little digging and it turns out since Qt 4.8.6, support for versions of Windows before version 10 was dropped. So instead of gambling with newer versions of Qt that just won’t work on my “old” development Windows machine, I have to count on the versions of Qt that will. And Qt 4.8.5 was the last functioning version that seemed to be supported by most Windows versions.