plukaduck
That's what manufacturer says about the housing:
With this housing, a whole new world of applications opens up for your standard SLR camera: Inside the housing you can now take the camera safely canoeing, snorkeling or even diving, up to a depth of 20 m / 60 ft.
As you descend, the air is pressed into the camera. Due to this, the pressure inside the housing will remain the same as the surrounding water pressure. (this is the reason why ewa-marine housings are so safe to use: implosions are impossible) Due to this, we have to start the dive with a suitable amount of air inside the housing. The foam pads supplied with the housing are part of this air "reservoir" and additional air should also be blown into the housing, via the valve at the rear, to ensure that the maximum potential volume is being utilised.
So, accordingly to above sentences there is no pressure problem. At least shouldn't be and I didn't experience sympthoms you described
You're right thare are better and more reliable housings but, firstly, I'm not going too deep - 10 meters is my limit, secondly, 390 aussiebucks vs. 1200 US bucks makes the difference for me - I'm a casual snorkeler and I'm not a diver at all. When I'll decide to dive I'll buy proper housing