I know that it happens to even the best bowyers, but as nice as you make and tiller them, I wouldn't worry about it too much, goat.
A couple of years ago I had one break on my tillering tree. It was hickory backed elm and it split where I'd filed a temporary nock on the top limb. It split all the way through the handle and down into the bottom limb but stayed intact, no flying pieces.
It sounded like a .22 shot and yeah, I pretty much jumped out of my skin and called it a day after that.