[lotech]

That sounds weird to me, my one which I believe is the first version worked so far so good even after I dropped it on the floor, I found the lens mount little loose and I fixed the screws, the only problem I found is purple fringing in high contrast scence even stopped down, other than that no other issue.

[cyberjunkie]

That sounds weird to me, my one which I believe is the first version worked so far so good even after I dropped it on the floor...

I own the same version. It is said to be less sharp than the second type with the red ring, but it also fringes a bit less.
Given the current manufacturing standards, I'm fine with the build of the Samyang's. The 85mm and the 14mm are good, the 24mm and 35mm are great.
Allowing some tolerance cuts the production cost/time, and gives us lenses that will always reach infinity, no matter how extreme the temperature. That would be a severe problem.
I didn't adjust any of mine, but I would have done that if it really was the case. I almost never trust the infinity stop, and with fast lenses I always use enlarged Live View, or do some focus bracketing, so if a lens is slightly off it would not cause any real problem.