ExpandCollapse Column width not working

[marco]

I have a very simple grid

 

<telerik:RadGrid ID="GrdCourses" runat="server" OnNeedDataSource="GrdCourses_NeedDataSource" OnDetailTableDataBind="GrdCourses_DetailTableDataBind" AutoGenerateColumns="false" MasterTableView-ExpandCollapseColumn-HeaderStyle-Width="50px">
    <ClientSettings AllowDragToGroup="false">
        <Scrolling AllowScroll="true" UseStaticHeaders="True" />
        <Resizing AllowColumnResize="true" />
    </ClientSettings>
    <MasterTableView DataKeyNames="ProductPlanID">
        <Columns>

 

I was thinking that MasterTableView-ExpandCollapseColumn-HeaderStyle-Width property was there to set the width of the ExpandCollapse column... but it has no effect at all.

The skin has been set to tBoostrap in the web.config.

No other CSS are applied

I'm using v 2017.1.228

 

Anyone knows a workaround to this bug?