I have just downloaded and tried the kit without the Wii Drums for the sake of the experiment.
It seems there is a difference between Apple's drum kits and Boldt's.
The ones from Apple do last even when a short note is played, whereas Boldt's do stop as soon as the note is released. I think this has to do with the way the virtual instrument is configured (I guess his instruments are based on the EXS sampler, which has an option to let the sample go through the end even for short notes.)
I think the best would be the let Boldt know about this issue as it would benefit to every of his users.
Thanks for letting us know about this nice collection of virtual instruments!