Keyboard Navigation in filter row of ListGrids doesn't work for DateFields

We have some problems with keyboard navigation in the filter row of ListGrids. If one of our columns is a date field, a DatePicker symbol is shown in the filter row. We are able to step over the DatePicker symbol with the tab key, but the other direction (shift-tab) does not work. The focus does not get to the column prior to the date column.

SmartClient Version: 10.0p_2015-01-10/PowerEdition
Browser: Firefox 26.0