After the upgrade from 1.1.2.0 to 1.5.0.23, some of the buttons began to look weird-as if blurred along the contour:

On all buttons same style:
<Style x:Key="BtStyle" TargetType="{x:Type Button}" BasedOn="{StaticResource SquareMetroButton}">
<Setter Property="BorderThickness" Value="1" />
</Style>