Hydraulic hose end cutting

Without seeing your hose, I would suspect that there is nothing wrong, nor are there any manufacturing defects. Depending on the exact rating of the hose, and the type of reinforcement, after being cut, the hose may spring to a more hexoganal shape
(does the rest of the hose remain circular?)

Hoses are made up of several layers and this is very typical. The initial layer is for corrosion protection, the middle layers are for strength/reinforcement, and the outer layer is for weather/abrasion/cutting/... protection from the elements and usuage. What you are seeing in first 3-4mm is simply the corrosion protection layer and nothing is out of the ordinary.

http://www.alibaba.com/product-gs/210078432/SAE_100_R12_hydraulic_hose/showimage.html?

What did you cut it with ? Would be my question. If it is uncut and new then it is just the way it is made.

When they run the hose thru the braiding machine to apply the reinforcement wire the tightness of each spool of wire can cause small changes as the braid on the hose advances. This is no big deal unless the wires are too tight and then cuts into the hose it is meant to protect or reinforce when pressure is applied.

It takes a very good braider machine operator to keep the tension on each spool of wire the same when running 10 or 20 braiding machines at one time.

It is because of the wire. The braided wire is under tension and slightly bonded to the rubber jacket. When you cut the hose the tension in the first section is lost and the bond broken. The hex comes from the uneven release of tension.

My hmble opinion...