i've found that when 100% infill is set, simplify still print in 2 times normal infill and top/bottom infill. I post a screen for explanation.
As you can see there is the bottom infill, and a little border that is the infill. If set <100% it's ok this way but if i set to 100% i expect that it will print togheter with bottom infill. I hope i've explained the concept. Sorry for my bad english!