Do you guys have notice a neutral between 5 and 6 gear?
Ah ha! What you have found my friend is called false neutral. It usually means that gears and engaging levers are spinning with sub-millimeter clearance between them. Usually it mechanical reasons, from worn gears to a bent shift fork to poorly adjusted shift linkage to just rider error (not a positive enough shift) Sometimes while you're in it, it'll sound like loose nuts and bolts chattering inside the transmission. Pretty common in cassette type close ratio transmissions.
Usually isn't. Does it happen more than once? Does it happen while you're just commuting? Usually when you're in a relaxed state, you don't use as much force and you don't bump the shifter hard enough... As long as you caught it right away, Minimal damage so you should fine.
my rc51 has similar problem. it's like i shift but miss the gear. when it happens i down shift before up shifting again. this happens about once or twice on a 200 mile ride in the back country with a fair amount of shifting involved.