Hi Dougal,
I am new to this forum and this is my first post, I am an italian archer.
I think that your limb's breakage is not common but it may happen after a string failure, the limb tips free of the string moved at high speed forward putting enormous stress on the limb bolt
which was the only point that secured the limbs to the bow, no wonder they broke, they are not made of stainless steel or titanium and of course they are not meant to take that kind of abuse which is particularly severe on a high speed limb.
What to do to avoid in the future?
Well, the string is critical, in the old days of kevlar archers passed most of their time string making, nowdays with the new string materials we think strings last forever, that is not true, my advise to you is to make your string yourself, sizing the end loops to match the limb tip groove, I find that commercial strings loops are too big, since they must fit different make of limbs.
bye.