I assume you mean the sample gets cut short or truncated by clipping and not exceeding the sound floor of the sampler and digitally clipping. If that's correct I believe the sequencer doesn't play nice with gated loops in SP's, I had this issue yesterday on my 404sx and had to switch the sample to one shot mode to have it play in the sequencer properly. I pretty sure when it's gated and the sequencer loops back around it wants to turn the sample off which can suck, but on the plus side I do believe this weirdness can be used as a type of mute which is mention in the 404 tips and tricks section by Lord Beatjitzu.