silverlight - Closing AutoCompleteBox loses Focus to Browser -

i've extended autocompletebox of silverlight , overridden ondropdownclosed event handler. works expected except component looses focus browser once dropdown closed.

what have change in order keep it?

here's code:

namespace itpole.sphere.application.core.controls {      using system.windows;     using system.windows.controls;     using system.windows.media;      public class customcompletebox : autocompletebox     {             public static readonly dependencyproperty selectedatcloseproperty =             dependencyproperty.register(                 "selectedatclose", typeof(object), typeof(customcompletebox), new propertymetadata(null));          public object selectedatclose         {                         {                 return this.getvalue(selectedatcloseproperty);             }              set             {                 this.setvalue(selectedatcloseproperty, value);             }         }          protected override void ondropdownclosed(routedpropertychangedeventargs<bool> e)         {             base.ondropdownclosed(e);             this.selectedatclose = this.selecteditem;          }          protected override void ontextchanged(routedeventargs e)         {             base.ontextchanged(e);              if (string.isnullorempty(this.text))             {                 this.setvalue(selectedatcloseproperty, null);             }         }      } } 

and usage in xaml:

<controls1:customcompletebox x:name="portfolioautocompletebox"                              grid.column="1"                              grid.columnspan="2"                              grid.row="1"                              margin="2"                              datacontext="{binding portfolio}"                              style="{staticresource defaultautocompleteboxstyle}"                              itemtemplate="{staticresource descriptionitemtemplate}"                              valuememberbinding="{binding description, mode=twoway}"                              selectedatclose="{binding value, validatesondataerrors=true, mode=twoway}"                              itemssource="{binding values}"                              text="{binding text, mode=twoway}"                              behaviors:autocompleteboxbehaviors.populatingcommand="{binding populationcommand}" /> 

what version of silverlight using? works me v4.