Setting up TabBar of TabPanel breaks layout

[mhd]

I m using Ext.net TabPanel to display my view that looks like below:

 Html.X().Viewport()
                          .Layout(LayoutType.Border)
                                          .Items(        Html.X().TabPanel()
                                                         .ID("upperPanel")
                                                         .Region(Region.Center)
                                                         .ActiveTabIndex(0)
                                                         .Collapsible(false)
                                                         .Layout(LayoutType.Fit)
                                                         .TabBar(Html.X().ToolbarFill())
                                                         .Items(Html.X().Panel()
                                                                         .ID("mapPanel")
                                                                         .Title("Map")
                                                                         .Layout(LayoutType.Fit)
.DefaultAnchor("100%") 
.ItemsFromPartial("_mapView")
        )
        )

It is quite simple a viewport with tabpanel contains one panel. The problem is mapPanel is not well displayed and didnt fit all the tabpanel with Chrome (no problems with FF and IE). However once i comment this line .TabBar(Html.X().ToolbarFill()) mapPanel will be displayed properly. So how can i configure TabBar with TabPanel without breaking layouts.