>    i<cr>
>    Hello world<escape>

>    Hello worlD

I suspect that the escape key is sending some multi-character sequence
involving a tilde.  Try ktracing vi so you can see exactly what it's
reading from the tty.

_Fixing_ it is another story entirely, of course.  I have no
suggestions for that, though I hope the above will at least get you
looking in the right place.

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