Curse resistance affects both the amount of items cursed and the duration of the curse. If you have no curse resistance at all and are hit by a regular curse, then you will have 2 weapons and 3 vial slots cursed for around 40 seconds. If you have around 4 bars of curse resistance total and are hit by a regular curse, you will have only 1 weapon slot cursed at random and 2 vial slots cursed at random for about 30 seconds.
Curse resistance also affects the % chance of receiving a curse when using a charge attack from the faust or gran faust. I do not know these numbers off-hand, but it is possible to become 100% immune from self curse given enough curse resistant items.
This is just for regular curses, the penalties from strong curse would obviously be much higher, but I don't know any specifics right now. And although I haven't come across a weak curse yet (or havent paid enough attention), but I'm sure there's something that can apply a weak curse out there.
Happy fausting ^^
Its a bug you have, curse curses 2 weapons < if you have 3 you will have 1 un-cursed but i dont know about 4> and all but one of your vials unless its a monster curse, then it depends on the strength of thier curse, if its from faust, its always the above stated