Alt and shift keys doesn't work in RichTextBox just for the time

Question

It's a strange case but I don't even know how to debug this problem. My program takes two input languages (English and Arabic), when I first run the program and press any English letter then press Alt+shift to switch the language it doesn't work! then when I press Ctrl+shift to switch the direction to RightToLeft then try Alt+shift again it works! and still working for all cases after that.

actually it may be my code that causes this problem but I can't debug it! I tried.

Note: In a new RichTextBox without code it takes Alt+shift normally but it doesn't accept Ctrl+shift so I added if statement to make ctrl+shift work but it's not the reason of the problem because I tried to remove it and the problem remains

Note2: I don't know if changing selection start and selection length causes problems because I am changing them a lot in myFunction but return them to the previous status at the end of function.

my code to make ctrl+shift work

    Private Sub RichTextBox_KeyUp(sender As Object, e As KeyEventArgs) Handles RichTextBox.KeyUp
        Try

            ' if Ctrl and Shift are pressed then change text-align ( shift+ctrl OrElse ctrl+shift)
            If (e.Modifiers = Keys.Shift OrElse e.Modifiers = Keys.ShiftKey) AndAlso
                (e.KeyCode = Keys.ControlKey OrElse e.KeyCode = Keys.Control) OrElse _
 _
                ((e.Modifiers = Keys.Control OrElse e.Modifiers = Keys.ControlKey) AndAlso
                (e.KeyCode = Keys.Shift OrElse e.KeyCode = Keys.ShiftKey)) Then

                If RichTextBox.RightToLeft = Windows.Forms.RightToLeft.Yes Then ' if align is rightToLeft 
                    RichTextBox.RightToLeft = Windows.Forms.RightToLeft.No ' then make it LeftToRight

                Else
                    RichTextBox.RightToLeft = Windows.Forms.RightToLeft.Yes
                End If

                RichTextBox.SelectionStart = RichTextBox.TextLength
            End If

            ' Calling subroutine myFunction
            Call myFunction()

        Catch ex As Exception
        End Try
    End Sub