Since this thread is resurrected, I would add my experience for consideration.
I purchased a police trade-in Model 64 NY-1 that behaved much like that described by the OP.
A discussion here ensued, in which short stroking was mentioned.
After a bit of fiddling, I was able to capture the hammer at the point of release. Absolutely short-stroking.
A trip to the mothership and all was fine.
