Mr. Possumhunter:
Chances are that the half cock notch has been removed. This is often required if someone has tried to lighten the trigger pull by stoning off the lip of the sear notch. The sweep of the half cock notch has to be below the sweep of the sear notch. This is required so that when the sear comes out of the notch, the half cock notch can pass under the sear as the hammer falls.
What happens when the sear notch lip is shortened, it tends to put the sear notch and the half cock notch in the same sweep. Then when the sear comes out of the notch it is not above the half cock notch. Now when the half cock notch swings by it collides with the sear tip.
This situation is most easily dealt with by reducing, or removing entirely, the half cock notch.
The moral of the story is that to reduce sear engagement, build up the bottom of the sear notch, not cut down the top.
Glenn