Yes, I can understand a penalty if you do not mine continuously but it should be around 10%, not that you lose everything. What is happening if my rig breaks down or I'm without electricity?
How do I know that is not the pool operator who took my bitcoins, without sharing with the other pool members?
It's not a penalty. You don't get penalized for mining intermittently. Your
expected payout is exactly proportional to the number of shares you submitted. But the actual payout varies due to the random nature of block finding. Like I said, you were unlucky, you could just as well have received much more than the average.
There's probably some work to be done wrt providing the statistics necessary to verify everything is done honestly. It will probably be easier if the pool switches to a lower variance method.