shell command to outer screen session causes instability

With screen on my remote machine running inside screen on my
local machine, When I go into command mode on the local (outer)
screen session and run a shell command, this works fine.

However it has the undesirable side-effect of affecting the terminal
emulation in the inner screen from then onwards. Recently also
strange behaviour with the key bindings.
(the arrow keys started to behave as if they were <alt-arrow>

How might I avoid this undesirable side effect?

Thanks for any suggestions (or answers).

-- 
Eric Smith