Looking at the first picture you have (with your leg), it appears that the hinge end of the tab is by your leg. So, in essence, our "view" is from behind the tab and it would be attached to the boat where your leg is. However, what is confusing is the 'drop tab' in your right hand. The angle of that doesn't seem to match up with the second pic?
However, going on the first premise... If that is correct, it appears one of two things has happened.
1) The water pressure acting on the tab caused the center of the tab to bulge upwards - whereas the spot where the ram mount is stays put. I find this highly unlikely - I have, personally, never heard of this happening. Not saying it can't, but it would take an IMMENSE amount of pressure to cause that.
2) Something was lodged under the tab and when the "down" button was pressed, the ram extended, forcing the back edge of the tab downward, while the rest of the tab stayed put.
Logically speaking, #2 make much more sense. Especially since it has happened twice to the port side and not at all to the stbd side. An example would be if the tab was extended and then set onto a bunk trailer (where the bunks sticks out a little bit past the transom) or the boat was set onto a rack with the tab extended and the rack stuck out a little too far. OR... someone extended the port tab while the boat was sitting on said trailer/rack.