c-i stopped working - need advice on further debugging

[Marco <lists homerow info>]

Hi,

mc used to work for years, but since recently some minor annoyance
started to manifest: c-i doesn't work any longer for changing the
panels, tab however works. Pressing c-i and nothing happens.

I observed:

- Creating a new user and c-i works as expected. So I assume a
  configuration issue on my side.
- Renaming ~/.config/mc and starting mc still results in c-i not
  working, so apparently not a configuration issue in mc.
- Changing the user (su [user]) in my current terminal and c-i works
  for the other user.
- Leaving X and using a native terminal and c-i is still not
  working.
- Opening mc, and typing cat c-i results in a tab, so the key combo
  works in general.
- I deleted ~/.local/share/mc and ~/.cache/mc to no avail.

I'm at a loss. It used to work in the past and it works for another
user (so no issue with mc) and I basically ruled out an issue with
my configuration. Still something is wrong.

Any nudge in the right direction appreciated.

Debian Linux 4.13.0-1-amd64
GNU Midnight Commander 4.8.19

Marco