I use Qsynth 1.0.3 on Fedora 41.
In Qsynth, I added 2 SF2 soundfonts. I added an offset of 1 for the second soundfont. The channels are save as 'Guitar". The set up is the following:

After I hit play on Tuxguitar set up as a MIDI sequencer, the channels configuration is switched to this one.

Is this a bug or maybe I am missing something ...