Yamaha DTXpress/DTXplorer/DTXtreme

I have a standard DTXpress III setup with an additional crash cymbal 
on input 9/10. I have noticed that if I play leg strokes (heel down, 
beater ends up well off the pad surface) as opposed to foot strokes 
(toe down, beater ends up in contact with the pad surface)the kick 
drum sound doesn't trigger - i.e. the harder, more positive stroke 
which should be less liable to cause false triggers doesn't trigger 
a sound whereas the lighter stroke does. Also when I play in 
a "live" situation with external amplification, the kick drum sound 
occasionally fails to trigger if I play either of the crash cymbals 
in combination with the kick using either of the above kick stroke 
techniques. I have looked in the archives & it would appear that 
others have discovered similar anomalies with DTXpress kick 
triggering. What I would like to know is: has anyone managed to 
solve this riddle & if so is there anything I can adjust to resolve 
this issue?