I was getting near my 2000 character limit so more info.
This is my sporter with the shop made trigger and unmodified sear and original spring( not modified by me anyway). Mentioned with photos in this thread:
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Some of the build is documented here:
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Checking with things later when I was not as rattled, I found I could pull the trigger till the first stage easy pull was complete and up against the 2nd stage releasing the trigger it did not return to the forward position. Lack of lube, weak spring or normal? What say you Krag experts? Pulling the knob back or putting it on safety did allow the trigger to return forward. In the other thread it was mentioned that bolt lift could cause an unintended discharge with a defective or modified trigger sear assembly. So I lifted on the bolt and sleeve with the trigger pulled to the end of the first stage, it did not discharge.
  Right now I am questioning whether I lubed the knuckle on the sear or anything else in the trigger assembly. The sporterizing project took a couple of years with hundreds of assemblies and dis-assemblies. Not sure now on that final time.
Right now the trigger at rest is centered in the trigger guard opening with easy play from side to side, not sure if the sear also has side to side play.
I put the rifle aside cocked and on safety and intend to let it sit for a couple of days to see if the failure will repeat.
Sure wish I had put it down then and analyzed it when I was not rattled. I might already have a cause and be fixing it. Right now I do not want to take it apart and do something that almost cures it then I fails again in 1000 cycles.
The Krag trigger assembly is robust and should be problem free, so this is not a normal problem. If others have had similar problems and found a cure, we need to hear it for everyone's benefit.