with windows10/2k DPI/14 inch screen ,when show the gridview gridline,the line is different.
the other things,when the tabitem is selected,the dropdownmenu can't mark the selected item.
look the attach files!
Regarding the first reported issue - we believe that is caused by the default WPF rendering of 1px borders which we use for the gridlines.
Regarding the second reported issue - RadTabControl does not have built-in logic to display the SelectedTab in its DropDownMenu. However you could achieve that effect by using a custom style for the DropDownMenuItem. In the custom style you will need to bind the IsChecked property to the Header of the DropDownMenuItem and the SelectedItem of the TabControl using MultiValueConverter. If you need more help with this, please open a support thread referring to this feedback item.