Re: skew
Apallix, you should read designer_ec's original question carefully. He states that the circuit timing works and all setup and hold times are met.
You are confusing local skew with global skew, and you are also confusing a skew limit with actual skew.
Let us say, to take your example, that you design your circuit with a skew margin of 50ps. This does not mean that every flop-to-flop delay is at the critical edge of meeting timing (slack = 0). There are many many flop-to-flop delays that have plenty of positive slack, so they can tolerate a lot of local (adjacent flop) skew and still work.
It is typically only the critical path that has zero slack, and there you want the skew from one flip-flop to the next to be less than 50ps, but the global skew can be much bigger.
The global skew measures the difference between the earliest and the latest arrival times at any flop in the clock - even if there is never a signal that goes between them!
So you can easily violate your global skew limit and still have a circuit that works perfectly well. Think about it.