PATH not set for root on Buster

I understand this is a Debian problem, not a TDE problem, however: On one machine I have installed Debian Stretch + TDE; no problem. On the same machine I installed (on another partition) Buster + TDE. Seems to work, however most commands don't work from konsole with su. The reason is that the path does not contain important directories. Now the following I don't really understand: The path is ok in the different files I could check. I've added "export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin" to /root/.profile but it does not work. The result is that a command such as dpkg -i or dpkg-reconfigure does not work, until I issue the export PATH= directly in konsole Debian is fresh installed with netinstall. This is really inconvenient, so of there is no way to cure it I'm going back to Stretch. Thierry