no offence to you kyle, have one of your manifolds and love it, works a treat (after some mods)...
but every one of your manifolds that i have dealt with have boost creep problems and there have been several, this is not a one off
problem seems to be a combination of manifolds being so efficient at the collector, 90 degree angle of the gate pipe off the collector and size of pipe used for this pipe. its a simple fix.
it seems unreasonable that the pipe used to connect the gate by you is usually much smaller than the size of gates people use, you should look at putting a larger 50mm pipe on a upwards angle, going slightly with the flow (not 90 degrees to the direction of flow).
on topic now: yes gate placement is stupid in this case and making the problem very bad, as kyle said mount the gate close to the manifold not down low...