vim-patch:7.4.427

>Problem:    When an InsertCharPre autocommand executes system() typeahead may  be echoed and messes up the display. (Jacob Niehus)
Solution:   Do not set cooked mode when invoked from ":silent".

https://code.google.com/p/vim/source/detail?r=v7-4-427

The heck? Who'd want to call `system()` every time they insert a char!? I just *had* to look up the source of this problem: https://groups.google.com/forum/#!searchin/vim_dev/InsertCharPre$20autocommand$20system/vim_dev/1CEVoPZ71gY/7NAqToSYrYMJ

Run this and you might be a little surprised: `nvim -u NONE -i NONE -c 'autocmd InsertCharPre * call system("sleep 1")'`

We don't share the relevant code with vim anymore, but the fix translates well to nvim.