If the text is too long in a RadMenuItem, when you mouse over the menu items, part of the highlighting isn't visible. The following code demonostrates. See Capture.png to see that part of the highlighting is missing. The rendering problem seems to be browser independent. I tested it using IE, Firefox, and Chrome and they all have the same problem.

<telerik:RadMenu ID="RadMenu1" runat="server" Width="100%">
    <Items>
        <telerik:RadMenuItem Text="UBorrow">
            <Items>
                <telerik:RadMenuItem Text="Borrowing Transaction Counts by Borrowing Library" NavigateUrl="~/BorrowingTransactionCountsByBorrowingLibrary.aspx" />
                <telerik:RadMenuItem Text="Borrowing Transaction Counts by Is First Lender Filled and Month"
                    NavigateUrl="~/BorrowingTransactionCountsByIsFirstLenderFilledAndMonth.aspx" />
                <telerik:RadMenuItem Text="Cancelled Lending Transaction Counts by Cancellation Reason"
                    NavigateUrl="~/CancelledLendingTransactionCountsByCancellationReason.aspx" />
                <telerik:RadMenuItem Text="Filled Borrowing Transaction Counts and Average Turnaround Times by Borrowing Library and Lending Library"
                    NavigateUrl="~/FilledBorrowingTransactionCountsAndAverageTurnaroundTimesByBorrowingLibaryAndLendingLibrary.aspx" />
                <telerik:RadMenuItem Text="Filled Borrowing Transaction Counts and Average Turnaround Times by Borrowing Library and Month"
                    NavigateUrl="~/FilledBorrowingTransactionCountsAndAverageTurnaroundTimesByBorrowingLibraryAndMonth.aspx" />
                <telerik:RadMenuItem Text="Filled Lending Transaction Counts and Average Turnaround Times by Lending Library and Borrowing Library"
                    NavigateUrl="~/FilledLendingTransactionCountsAndAverageTurnaroundTimesByLendingLibaryAndBorrowingLibrary.aspx" />
            </Items>
        </telerik:RadMenuItem>
    </Items>
</telerik:RadMenu>