MacOS: animated SVG data has a shadow when it is put in a QDialog

There is a problem with SVG data in our application, after some analysis and research, we suppose this should be a bug of Qt. Therefore, we try to create a simple example to reproduce the problem. We put an .svg data in a class inherited from QDialog and run the app. The result is as follows, there is a shadow of the first circle on animating (while the SVG data does not have any error itself).

I have attached the simple source code and the Qt configuration to simulate the problem. 

In this example, we use Qt 5.12 but you can test with the newer version of Qt (e.g 5.15), the problem still appears.

We have tried with other animated SVG data with another form (e.g. not circle anymore but triangle) but the problem is still the same. Some functions in the example are static (maybe unnecessary for this simple example) because in our app they are also static. But we think that does not affect the problem with SVG data here.

Please take a look at the problem whether it is a bug of Qt! 

Thank you very much!