Anything based on SimpleOpenNI (including NIMate) takes an age to initialise skeleton properly unless it can see full height (feet to head) in shot. When you get too close, frequently skeleton legs start to go whappy - skeleton doesn't like it when it can't work out where a limb is, and just makes something up, which often freaks out whatever the Kinect is driving... One of many reasons I avoid using skeleton and prefer depth blobs. Otherwise, you have to add your own checking routines to remove limb markers between your middleware and output, or disable whatever that limb is driving when the coordinates exceed screen / stage / world boundaries or just vanish.
