GTK+ interface, backspace is broken in the monitor console

this has been broken for over 2 years

Confirmed, this is indeed broken. I sent a patch with a fix to the mailing list:
https://marc.info/?i=1470900060-25821-1-git-send-email-thuth%40redhat.com

thank you

Fix has been picked up into the repository now:
http://git.qemu.org/?p=qemu.git;a=commitdiff;h=344aa283b89bec2af9761

Released with version 2.8