Overtyping the first half of a wide character with the
second half of a wide character results in display garbage.
This is because the trailing dummy is not cleaned up.
i.e. ATTR_WIDE, ATTR_WDUMMY, ATTR_WDUMMY
Here is a short script for demonstrating the behavior:
#!/bin/sh
alias printf=/usr/bin/printf
printf こんにちは！; sleep 2
printf '\x1b[5D'; sleep 2
printf へ; sleep 2
printf ' '; sleep 2
echo