Yamaha DTXpress/DTXplorer/DTXtreme

hi guys, got dtxpressII.great kit good sounds.having trouble setting 
up backing tracks (mainly percussion)i set up a percussion kit in 
user kits and dialed the sounds thru channel 6,sweet as.went to user 
songs and laid down a track,which worked well,dialed in my favourite 
kit and played along,no worries until i powered off the unit went 
away ,came back,powered up and went to play along with my newly 
created backing track to find all the percussion sounds had changed 
to piano freaking sounds.......Im quite new to electronic gear after 
20 years of accoustic kits and not used to the terminology used in 
the manual    please help