Control-Z hanging vi - Why

[Ken Goldman]

HW - Valid workstation running 4.1BSD:
Due to a keyboard which reverses the CTRL and SHIFT keys, users (including
myself) occasionally type ^Z^Z instead of ZZ to write and exit from vi.
This hangs the terminal - all characters are echoed but none have any
effect, not even ESC or ^C or ^D.  The only solution is to kill the
process from another terminal, losing the editing session.

Anyone have a better way out?