QPainter fillRect() transparency issue

Filling a paint device through QPainter.fillRect() with QColor(41,51,123,177) gives a completely different result compared to QColor(42,52,124,176). As shown in [color_issues.png] (which can be reproduced with [test_color.py]), the alpha/transparency settings are not honored when using fillRect(), but work when using QPixmap.fill(). Also, above/below certain threshold values, the color changes to pitch black.

[1][2]
[3][4]

[1] QPainter.fillRect() with QColor(41,51,123,177)
[2] QPainter.fillRect() with QColor(49,123,226,40)
[3] QPixmap.fill() with QColor(41,51,123,177)
[4] QPixmap.fill() with QColor(49,123,226,40)