Yamaha DTXpress/DTXplorer/DTXtreme

Hi all
 
I bought a DTXPREEII last week and while practicing (and improving 
my coordination) I noticed a problem/bug in the trigger module:

When I hit the HiHat and the snare at exactly the same time, there 
is no output from the snare. When I try it with all the Toms, it 
seems fine. I swapped a Tom with the snare and got the same problem, 
so it's not a problem with the pad.
 
I haven't changed any settings on the box itself, but reset to 
factory settings anyway. I also tried it with seperate drum kits.
 
Has anyone seen this problem? Can anyone reprodcue it?
 
Thanks in advance
 
Mark