Fixed it in my template but you should update your dll's etc. Currently it shows a combobox down arrow but should be a calendar grid like other themes have.
<
Path
x:Name
=
"Icon"
Margin
=
"4 5 4 4"
Stroke
=
"{StaticResource Icon_Normal}"
Width
=
"7"
Height
=
"7"
Data
=
"M0,0.5 L7,0.5 M0,2.5 L7,2.5 M0,4.5 L7,4.5 M0,6.5 L7,6.5 M0.5,0 L0.5,7 M2.5,0 L2.5,7 M4.5,0 L4.5,7 M6.5,0 L6.5,7"
/>
<
Path
x:Name
=
"IconChecked"
Margin
=
"4 5 4 4"
Visibility
=
"Collapsed"
Stroke
=
"{StaticResource Icon_Pressed}"
Width
=
"7"
Height
=
"7"
Data
=
"M0,0.5 L7,0.5 M0,2.5 L7,2.5 M0,4.5 L7,4.5 M0,6.5 L7,6.5 M0.5,0 L0.5,7 M2.5,0 L2.5,7 M4.5,0 L4.5,7 M6.5,0 L6.5,7"
/>