The first thing I would check is your bow's centershot. Make sure the nocking point and rest are inline. A quick way to check the horizontal aspect of it is to line up your string through the hole in the rest....are your sights inline with string, or are they off to one side? If they are off, you need to move the rest. This is a very rough way to help setup centershot, and I'm sure there are lots of guys here who can help explain both the vertical and horizontal setup much better than I can, but that is the first thing I would suspect.

I've shot a WB for three years and this spring I did some changes (DL) on my bow and suddenly I was loosing fletchings left and right. My coach looked at my bow and found out that the rest was out of whack. A quick adjustment and my fletchings stayed on!

Also, without knowing what type of arrows you are shooting, are all of them fletched the same way, do the fletchings line up and go through the same spots in the WB, or do nocks need turned so they are all the same? This could also cause problems for you.

Finally, and maybe the most obvious, check everything over for contact. Are the fletchings hitting something as they are shot (cable, cableslide, arrow shelf, the metal ring of the WB)? That would also cause fletchins to come loose as well.

Hope this gives you some ideas.