> this patch adds "Qucs-S", a GUI for different circuit simulation
Often GUIs have problems with finding icons, could you check whether qucs-s works in a pure environment?

> +    (propagated-inputs (list ngspice))

Propagation is not very robust (e.g. if run directly from the store with 
$(guix build qucs-s)/bin/the-binary), would it be possible to not 
propagate this? E.g., if you are propagating it because of not finding a 
binary, you could use substitute* to insert an appropriate absolute file 
name.

Greetings,
Maxime.