For input and output devices, the button for "Set as fallback" doesn't behave intuitively. It appears to be a normal button, which remembers its state (pressed or not). That leads to the situation described below.

— Initial situation
Sources (asterisk marks the default as reported by pacmd):
1) *
2)
Select source #2 in the GUI and click the "Set as fallback" button.

— New situation
Sources:
1)
2) *
Number 2 is now the fallback as expected. The button is now in a "pressed" state. By clicking it again, one might assume that source #2 will not be the fallback any more, as it's represented by the button moving back to the "unpressed" state. However by checking the pacmd output again, source #2 is still the fallback. The button can still be clicked to make it change its state, however it has no effect on the sources itself.

Would it be possible to change the button type to something that would represent the situation more clearly? Maybe even add "Default Source" or similar next to the source or sinks (input and output devices), to easier convey which one is the default (fallback).

Pavucontrol version 3.0.
Pulseaudio version 9.0.