Leaking to snorkel depth - flooded and broken camera

This case is a good all-weather protection and the camera can thus be used for example on the beach, and are protected against shocks. Because it is so cheap, would the five stars. But as underwater housing, it is useless and I have therefore sunk 200 Euro.

I bought the case last year and was thus a total of four times with water. The first time I tested in the sink if the housing holds tight.
Then I was three times in water, but never deeper than 1m. The third time I noticed after about 10 minutes a frantic blinking of the autofocus assist beam. After the "emergence" I find three drops of water in the housing. For the camera which has already passed, it was salt water, it spins around until only, then total failure.
Yes, I have checked the seal for foreign objects before each use.

I suspect there are already enough of Arising on swimming movements, higher pressure to let the case be minimal leakage, so that water can squeeze through the seal. Perhaps also the temperature of the water plays a role here, it was after all about 28 degrees.