If the grey tank vents in a location behind the propane sensor it seems like it could also contribute to the sensor going off. Methane gas is produced as a byproduct of anerobic decay which occurs in both the grey and black tanks, more so in the stinky ones.
I don't know of any resolution - although one owner did a nice job of extending to an external vent (Klem, see post #33 of that other thread) - but the result of the discussion with Reace, and comparison of installations, is that this vent inside a cabinet is deliberate, not an isolated accidental omission (although one may have been accidentally shorter than intended).