Do you clean your brushes?
And I don't mean just wash out the paint with water, but actually GET a brush cleaner like this product:
http://www.dickblick.com/zz057/02/ To ensure that no paint particals dry up and start weighing down the hairs of the brushes.
Also, when you paint with your brush, do you hold your brush and apply pressure to the model with the brush being held at a 90 degree angle, or do you use the sides of your brush to apply your paint holding it at more of a 60 or 30 degree angle range.
There are alot of very bad habits that many new painters pick up that makes brushes hook. My advice is to get a brush cleaner, and give your brushes a good scrubbing and see if they are savable.
Also, as a rule, don't buy GW brushes in the future. They are terrible quality brushes for the price you pick up on them.
Also, remember that Paint bushes WILL die out after quite some time anyways. If you have used these brushes through years of painting miniatures, then even the best brushes can die out after a long run. The best advice I can give is to just treat your burshes right, and remember to not just clean the brushes with water, but use the soap while cleaning them, as the back and forth motion of you running them through the soap should straighten out any bending from individual sessions of painting, but it will not fix long term damage to the brush.
Also, avoid the following bad habbits, as they ALL contribute to hooking brushes:
Forget to clean brushes thuroughly and have to "Scrape off" dried paint off the brush hairs
"Soaking" brushes for extended periods of time, as the tips will start to bend with the constant pressure, and water making the brush hairs more mold able.
Extended painting at sharp 90 degree angles
Using the wrong type of brushes for the paint you are using (I. E. a watercolor brush for acrylic painting.)
Constant drybrushing will hook the hairs of a brush as well.
Just keep these things in mind when your using any type of brush to avoid hooking as much as possible. But the big one is to PROPERLY clean your brush after every use of it.