Spectra break phenomenon

At the risk of sounding like a real meat-head I have a question
for those of you (I presume just about everybody) who use Spectra,
or similar, line.
Here is the setup:  Spectra 150lb line.  Yes, it is sleeved!  Heavy-duty
swivels attached to sleeving by 125lb nylon traces (the intention was
that these traces, only about 8-10 inches long, would break before the
Spectra.  Also they make matching line lengths alot easier).

bridle -LH- swivel -LH- braided trace -LH- looped sleeve (LH=larks head)

Here is what happens:  I have broken this line on two occasions.  First
was with my foil on a windy, windy day.  I reckoned that I took the line
beyond its limits and BOTH lines broke.  I found that surprising but
at least it saved me from Death by a Thousand Tangles.  The funny thing
was that they broke about one inch from the sleeving at the kite-end.
I re-sleeved my lines and made up some new sacrificial traces from
110lb braided nylon.
The second time they broke was on a milder day when I was flying my
Fire Dart.  Again, both lines broke about one inch from the kite-end
It strikes me that:
- Both breakages happened after many, many hours of flying.
- In both cases I re-sleeved, re-tuned for length, and carried on
  without any more breaks.
- My sacrificial traces survived twice (great plan, huh?). :-(
- Both lines went on each occasion.
- The second incident happened in mild-ish weather (read: not much
  pull from the kite).
Is this coincidence?  Am I witnessing a known phenomenon?  Have I
offended some little-known String God?

Any half-believable explanation gratefully received!

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