VFO A and VFO B do not accept different bands at the same time

Since what is supposed to work must work, after your observations, I started troubleshooting by simply resetting the radio (6400) - and lo and behold: now it works, with two pan adapters, as recommended! It's a bit surprising that this helped, since it already worked before with SmartSDR. Perhaps the touchpad was acting up with the numeric keypad, because after entering the first digit of a new frequency in VFO B, the display always jumped to the previous value in the same band as A and vice versa. However, now the problem is solved, ufb! mni tnx for the encouragement here, hi…