CheckBox Indicator Image bug

[flyaway9109]

Look at the picture, CheckBox in a RowLayout, set the indicator width a Image,
but with diffrent height setting in CheckBox, it show diffrent
height: 20 (the image top show one more pixel)
Layout.fillHeight:true (Image show correct)
But if checkBox not in RowLayout, use height:20 will show correct image
Anyone know why? thank you