It's caused by the time-stretch engine. Some meta-data in the wave file tells the program to stretch the sample to one certain time value, so it stretches it automatically. Just set the TIME knob to zero, and it will be alright.
My suggestion: right click the waveform of the sample and choose EDIT, then set a full-length loop by dragging the start/end lines. Then save the wave file, overwriting the former. Of course you can turn off looping in the channel properties if you don't need it. This usually solves the problem permanently.
Hope you solve the problem. 
Quoted from ""The Enforcer"" 
