Ctrl-alt-delete in syscons pause/scrollback mode breaks system

Today I came back to my computer and realised I'd left ttyv0 in
history/scrollback mode, with scroll-lock enabled. To see what
would happen I pressed Ctrl-Alt-Delete to reboot and was surprised to
see that it seemed to get partway through the process but it never
rebooted: the other ttys were killed and I could still break into the
debugger but otherwise the system was unresponsive.  Trying to repeat
it after rebooting I ended up with a system that won't even break into
the debugger. Is this expected?

-- 
Bruce Cran