hold button to set output level

I use PC keyboard to control mobius

I can decrease the output level with this script

Code:

---

!name R_4

for 4
set output output - 10
endif
next
end

---

but I can't do it by hold function with this script

Code:

---

!name R_4
!sustain 1000

Label Sustain
if sustainCount = 1
for 4
set output output - 10
endif
next
end

---

what's the problem?