xaml - WPF: DatePicker text centered vertically -

i using datepicker in app defined such:

<datepicker width="200"             margin="20, 20, 20, 0"             selecteddate="{binding periodenddate, mode=twoway}" /> 

here how date picker displayed:

how can date (4/22/2015) center vertically in textbox (the dotted line around date actual textbox boundary)?

i have tried setting both verticalcontentalignment , verticalalignment center doesn't affect date centering.

if dig date picker using snoops can see element called part_textbox within datepicker. if change part_textbox verticalcontentalignment center, text centered (is set stretch default). however, not know how access subcomponent change it's verticalcontentalignment