Height of titlebar changes when all buttons are disabled

The height of the titlebar in a window changes when all buttons are disabled. The titlebar has a greater height when at least one button is visible:

<themes:WindowChrome.Chrome>
<!-- At least one button is visible in the titlebar -->
     <themes:WindowChrome HasCloseButton="True" 
                          HasMaximizeButton="False" 
                          HasMinimizeButton="False" 
                          HasRestoreButton="False" />
</themes:WindowChrome.Chrome>

The height gets smaller when I deactivate all buttons:

<themes:WindowChrome.Chrome>
<!-- All buttons disabled -->
     <themes:WindowChrome HasCloseButton="False" 
                          HasMaximizeButton="False" 
                          HasMinimizeButton="False" 
                          HasRestoreButton="False" />
</themes:WindowChrome.Chrome>

Is there a way that the titlebar keeps it height? I don't want that the titlebar shrinks when I deactivate all buttons.