[ZAKO the GREAT]

i guess it might be something to do with the tool you're choosing. like, when you choose paint brush, even with 100% opacity, hardness & flow and 1px, even a single click, what i get it's a 4 pixel instead of 1.
00
00 = 1px

and i choose pencil tool with the same settings (no hardness), what i got it's a solid, 1 pixel block.

0 = 1px

i dunno, since i don't have my wacom with me now, what i guess it's either the tools you chose, or the pressure of your wacom pen when you use it as it'll determine the color it to get the real "pencil on paper" kind of feeling unlike mouse.
hope it helps!