Kemper support did answer today: They say it is a bug.
They can not tell how long it will take, but they'll seek to address this problem as soon as possible and ask for patience.
Patience ... not one of my strenghts
This is quite a big bug in my opinion and concerns a basic function. Tone is directly affected...
And what is not clear to me, if in general the cab section is affected (changes tone) dependent on the loaded amp section? So changing cabs in the Kemper would be a total different approach to what I know from other devices. And a specific "favourite" cab copied to other profiles or the use of converted IR would have to be seen in a completely new light?! Anyone with insight, how amp and cab section really "interact" here?