This is my Button:
<Button
Name="btnOk"
Content="OK"
Style="{StaticResource AccentedSquareButtonStyle}"/>
And the content
is always with lower case latter when using this Style
You should use
Controls:ButtonHelper.PreserveTextCase="True"
to prevent lower case (or upper case on other controls).
EDIT
There is a change in the Alpha release (the upcoming v1.2.0). It's now possible to change the case much more easier.
<!-- possible values are: Normal, Upper and Lower -->
Controls:ControlsHelper.ContentCharacterCasing="Normal"