GroupBox header text is cut off

I've tested it with everything that came to my mind and im not able to reproduce it. Please try the following:

<GroupBox FontSize="12" FontWeight="Bold"> 
    <GroupBox.Header> 
           <TextBlock Height="22" Text="Current Units (English)"/>     </GroupBox.Header>

Since the Header in the GroupBox is a TextBlock anyway, we do the stuff now by ourself and adjust the height a little bit