One thing I discovered on my TI's that may relate to your situation.
If you open the front hatch and look inside you will see the metal triangle brace setup is very strong to prevent side to side movement (you shouldn't have problems with that as long as you check it "often"). However if you study where the stresses are exerted from while the sails are propelling the boat "forward" you will discover the mast reciever acts just like a giant lever for the forward and backward forces. The pivot point is about a foot up from the bottom of the mast, you then have a 17 foot lever pushing forward (the sail). This create a backwards force at the base of the mast cup that is huge (could be several thousands pounds of force). Think about it, if you took an 18 ft pole and put a brick under it 1 ft up from the end, when you push down on the long end you can probably lift your car easily with the short end (17 to 1 ratio 200* 17 = 3400 lbs lifting force if I stand on the end ). Now if you look at what is holding the mast cup from forward to back movement you will see a tiny 1/4" stud that is all that holds the mast cup, and thats it.... If the stud breaks the hull bottom just pushes out of the way as it rises up and over the tapered pyramids with the brass insert inside.
above is a (slightly modified) excerpt plagiazed from a previous "kind of related" thread
I realize my TI is not normal with 265sq ft of sail, but alot of the same forces apply regardless how much sail you are flying. This video shows how I re-enforced the bottom of my mast cup to help counteract some of the extreme backward force going on down there. I have way over 2000 sailing miles with all my custom mods and extra sails installed (really hard miles at times (over 18mph)), and have never broken a 1/4 inch stud.
I laid in a 1/8" x 2" x 7 1/2" piece of aluminum behind the mast cup. I then built a dam with clay and filled in and around the aluminum piece with West Epoxy. The front of the mirage drive pocket is probably one of the strongest points on the boat. Of course the Epoxy does not stick to the plastic hull, so if you ever want to remove the brace, you just pop it out.
I'm not suggesting anyone re-enforce their mast recievers, I'm just describing what has worked well for me, and more importantly try to explain why those darn studs break, and the forces involved.
PS Pulling the sail really tight (like when sailing directly into the wind) can also snap that stud (in the forward direction)... (my fix doesn't help with that)
Hope all this helps...