I have seen on the Glock chat rooms that there have been many problems with Glock's "KB ing" mostly in 40cal. I have not seen any problems on the Walther site with this problem has any one herd of any with the P99
As you mentioned, Glocks, especially in.40 S&W, have been known to have kaBooms or kB's. The two culprits are bad reloads and people using unjacketed ammunition. The .40 S&W cartridge has a very small margin for error so it is very easy to over charge it when doing reloads. Also if the brass is weak because it has been used several times, you can have a serious problem. Additionally, Glock uses a different type of rifling than the P99. I think Glock makes use of polygonal rifling and that makes it more susceptible to fouling from lead. The rifling in a Glock means shooters should never use unjacketed bullets in it but many do because it's cheaper.
When talking about Glock problems in.40 S&W you have to remember that those guns are in the hands of a lot of people, many more than those who have a P99. A certain percentage will buy the gun and not know how to care for it or what is a do or a don't. Since there are many more Glocks than P99's, even if only 5% of the owners bang on their gun like monkeys, you would see a lot of posts about problems. I've read many reports where the shooter bought reloads at a gun show from a guy he never saw before or since and all of a sudden kaBoom. Many people who have had this happen will complain on the various gun boards that Glocks are poorly constructed or defectively designed or the cartridge is bad. They're just shifting the blame. It's not the gun design or the cartridge, it's the people.
The .40 S&W has very little room for screwing around and is tough on brass. Stick with quality factory ammo and stay away from reloads in this calber and you'll be fine.
A lot of the problem with the .40 also stems from it being such a new cartridge and not much knowledge on how to reload it. A couple of years ago, Hodgedon had printed a in their reloading manual 2 grains of powder over the limit for the .40!! This cause a friend of mine's Glock to kB!
I've heard of 1 P99 that has kB! And it was the fault of the owner. He had dumped too much powder in one case.
I've been reloading for my P99's (.40 and 9mm) since 1998, with no problems at all. If your going to reload I would suggest you buy a case gauge and check each reloaded round. It just takes a few more minutes of your time. Also, don't load to the maximum when using 180 gr bullets.
I also only use my brass for 5 firings, or if they look bad to me, they are tossed.