Anyway, considering that the issue was not present for the newly created user, one thing I would suggest that you try is to clean the mozc cache in $HOME for your real user account.
I.e.:
mv ~/.mozc ~/.mozc.bak
and relogin.
Does that possibly fix it irrespective of the presence of ~/.xinputrc ?
Thank you for the additional info. That's weird.
Anyway, considering that the issue was not present for the newly created user, one thing I would suggest that you try is to clean the mozc cache in $HOME for your real user account.
I.e.:
mv ~/.mozc ~/.mozc.bak
and relogin.
Does that possibly fix it irrespective of the presence of ~/.xinputrc ?