because it comes down to the design on the exhaust, if the exhaust is such that the cat and the bends and the dump, cause sufficient enough restriction in the system, the gas will want to flow through the gate, or to put it more presisly, it is forced to go that way, as it it easier to do so then to go through the turbine with has restricted flow. When the exhaust is so efficient, that it is easier for the exhaust gasses to go through the tubine and not the gate, as there is no restriction, that is when problems occur.
THIS IS A VERY COMMON PROBLEM, especially on SUBARUS and EVOS, when you change the dumps and get high flow or run no cats at all.
Not only is the exhaust a colprit, but if you run a FMIC, then the problem is worse. As cooler air means more dense air, esspecialy on cold morning, the turbocharger does not have to work as hard to compress the exhaust gases, and boost is made eaven easier. On such cold days with an FMIC, it is not uncommon to see a 5psi boost creep. This is to do with the fact that eaven though the gate is fully open, the gas is not going through it to regulate boost.
Now ther are things you can do, like getting an aftermarcket BOV, and regulating some of the boost that way, adding a restrictor plate in the exhaust, commonly done on RX7's. But the true fix is the internal gate, this is providing that you have tested things like the actuator and the arm and the gate for damage.
To port the standard gate, is no biggie, just a pain in the ass, as the whole turbo needs to come out, but seing as i can make nearly
210-220rwKw with a stock turbo, and the other mods i have, i am happy with keeping it as is.
Hope that anwsers some of the questions.