I think it stems form there layered limb design. When done right they are very tough and strong but it does not take much ( little air bubble for instance) and you have a spot that will crack out at some time. I did a google search after reading your post and found several hits in other forums talking about the very same bow and same splitting between layers you described. It has been several years back but had one of there bows with same layered limb tech. I did not have any problems with mine but sold it due to hearing of several others on the 3D tournament splitting between layers.
Frankly, I would not shoot it. Since you have already, have someone look to see if the two bottom limbs are drawing evenly and taht there is not even the slightest twisting in the limb. If not you should be ok to shoot it but the split will continue to open up. Now having said that and not being able to see you bow, I shot one on the 3d tournaments for a few years with a hairline split on the outside of one of the limbs it did not go all the way through and was right on the seam of layers. The limbs did start to twist and I continued to shoot it. The crack did grow from about 1 in to about 2 1/2 by the time I sold it. Judging from you measurements, are you saying 1 cm deep--that is probably about half of the limb. I would suggest having someone who works on Hoyts look at it and tell you if you can get a few more shots out of it before repairs.
