1) Login to SOGo webinterface with username + password only.
2) Open Preferences in SOGo webinterface.
3) Enable 2FA in SOGo webinterface.
4) Scan QR code (== secret) with TOTP app or device.
5) Copy TOTP code from app or device to verification field.
6) Store your change.
7) Logoff
8) Login again with username + password + TOTP code.
==> 2FA works correct.

9) Open Preferences.
10) Disable 2FA.
11) Store your change.
12) Logoff
13) Login again with username + password only.
==> 2FA disabling seems to works.

14) Open Preferences.
15) Enable 2FA again.
16) Do not scan the QR-Code with your TOTP app or device.
17) Copy TOTP code from app or device to verification field.
18) Store your change.
==> This should not work, as you did not scan the secret!!!!
Obviously the secret was not deleted by disabling 2FA.