MultiEffect's blur effect has error(maybe) color

The file `test_blur.zip` contains a simple test code that demonstrates an issue when using MultiEffect to blur a red circle on a green background. After blurring, there is a very noticeable black ring around the red circle.

The example tests two scenarios. In the first scenario, the red circle's rectangle has anti-aliasing enabled, while in the second scenario, it does not. With anti-aliasing enabled, there is a ring of black pixels around the circle, which might be related to the sRGB color space? I'm not an expert in this area, so I can only speculate on the cause. Since the source image contains black pixels, it's understandable that the MultiEffect blur results in black areas. However, in the second scenario, since anti-aliasing is not enabled, the source image does not contain black pixels, yet the blurred image still has black areas. Is this a bug in Qt? Or is this also related to the sRGB color space?

I tested using the Gaussian blur filter in GIMP, and it worked well. I have uploaded screenshots of the program running from `test_blur.zip`, as well as the secondary blur effect from GIMP on the test_blur program screenshot.

If this is not a bug, how can I achieve a blur effect in Qt without black pixels, similar to GIMP? Is it possible to do this via MultiEffect?