When I tested mine the same exact thing happened and I don't have the broken nipple.
The air would go....somewhere.
So fix it and see if anything changes. I think the engine stops in such way that on one of the cylinders you have valves partially open on both sides. I suggest that if anyone is doing tests right now, have a friend by the muffler to listen for the air coming out.
If you can't create a situation where 20 PSI is somehow pressurizing the intercooler and ajacent hoses, then I don't think it's a good test. Only once the pressure builds up close to this will you hear leaks.