A funny thing in ddd 3.3.12 (x86_64)

I encountered a funny thing in ddd 3.3.12 x86_64 (On Debian Jessie).
I was remote-debugging (serial protocol) ARM with
ddd -debugger "arm-none-eabi-gdb -x gdb-rpi"

I can't give any commands via the gdb-console. I can write there, but
ddd doesn't send it to the target, but just ignores it. And the local
commands don't work too well either.

Am I doing something wrong?

(gdb) help


Undefined command: "".  Try "help".
(gdb) help

{no response}