Change Windows 7 theme to Classic and run attached example. Start progress in application from the start button. See that progressbar doesn't animate. It works on on Qt 4.8.6. But not in Qt 5.2.1-5.4.1.
Workaround is to force style to "Windows" which is the same than default Classic theme.
Relevant commits: "Introduce (private) QStyleAnimation" 7501d55ae005cf9a155a6bcbeac468bfde40177d, https://codereview.qt-project.org/#/c/36369/