I face a very serious situation. By writing this question I hope that really professionals will express their opinion regarding to the problem I am going to describe. I have rep
I don't think it is a bug; I'd call it "undefined behavior". That means that if you try to animate minimumWidth, nobody can tell you for sure what is supposed to happen, and maybe the code has some optimizations or corner cases where sometimes it works, others it doesn't.
Anyway, minimumWidth and maximumWidth aren't supposed to be used to define what the size of a QWidget is, only what it must not exceed; i.e. they weren't designed to do what you are trying to do, so it can be called a bug. If you want to animate, you have to use a deterministic approach, which in this case is using the geometry property.