Grub interactive menu missing from Xen PVHVM DomU's 'serial console' output. All the other output is there - just the menu is missing?

[suse . dev]

I'm launching a Xen PVHVM DomU linux64 guest on a Xen 4.6.0 server.

I set up the guest to direct serial/console output to the shell/terminal I 
launch the guest from.

Works like you expect - all the detailed info you want scrolls by on guest 
launch.

Except for the GRUB MENU with the menu-entrly selections.  Unlike with a "real" 
serial console where I see the menu and cann interact with it, for the Xen 
guest I just see blank space


        Parsing config from test.cfg
        got a tsc mode string: "default"


                ( this is where you nomrally would see the grub menu)

           The highlighted entry will be executed automatically in 1s.          
       

                ( then it continues) 

        Loading Linux 4.4.0-5.gb56b151-default ...
        Loading initial ramdisk ...
        [    0.000000] Initializing cgroup subsys cpuset
        ...

I can enable

        sdl = 1

and then the grub2 menu and other output pops up in an X11 (bochs?) window, but 
that's not what I want.

I'm trying to get a 'plain text', interactive version of the grub menu to show 
up in the shell/terminal window. No X required.

The grub config in the DomU is

cat /etc/default/grub
        GRUB_CMDLINE_LINUX="root=/dev/xvda1 showopts noquiet console=tty1 
console=ttyS0,115200n8 systemd.log_level=info systemd.log_target=kmsg 
earlyprintk=vga,keep"
        GRUB_CMDLINE_LINUX_DEFAULT=""
        GRUB_DEFAULT=saved
        GRUB_DISABLE_OS_PROBER=true
        GRUB_GFXMODE="1024x768x32"
        GRUB_GFXPAYLOAD_LINUX="keep"
        GRUB_HIDDEN_TIMEOUT=0
        GRUB_HIDDEN_TIMEOUT_QUIET=true
        GRUB_SERIAL_COMMAND=" serial --speed=115200 --unit=0 --word=8 
--parity=no --stop=1"
        GRUB_TERMINAL_INPUT="console serial"
        GRUB_TERMINAL_OUTPUT="console serial"
        GRUB_TIMEOUT=10

What do you need to set/configure to get the Grub2 menu to show up in the 
terminal when using a 'serial console' output from a Xen DomU?