com.vaadin.addon.touchkit.ui.NumberField: hide keyboard after button click

Hi guys,
in my touchkit project I have a view with a NumberField field and a NavigationButton.
If I enter a value in the field, and then I click on the navigation button without “manually” hiding the virtual keyboard, I get a null value for that NumberField in the next view.
Why keyboard doesn’t disappear automatically after clicking on the navigation button?
Thanks
Fabio