LG 4163b +r problems

hi all,

have got 2 LG 4163b writers in my pc and have hit a small problem.
i can burn 2 ritek g05 -r’s at 4 or 8 speed using discjuggler or nero no problem.
when i try to burn my infinity 8x +r printables 1 at a time there is no problem at 4 or 8 speed using juggler or nero,
but when i try burning 2 at once i get a write speed of 1.7 speed with nero or juggler.
the disc’s burn great with the lg and will do 8 speed no problem in the nec 2510 0r 3520.
strange problem, does it sound like a firmware bug?