Two items; one is +50 points cold the other is - 50 points cold. They should cancel eachother out right?

the hide of the ancient white dragon can be referred to as 'hide ancient white'.
It is worth 10755 copper, and is of the 48th level of power.
It is armor worn on the body.
It is made of dragonscale and weighs 11 pounds 3 ounces.
When worn, it protects you against piercing for 16, bashing for 11,
slashing for 16, magic for 3, and the elements for 0 points each.
When worn, it affects your cold resistance by 50 points,
your save vs breath by -5 points, your hit roll by 1 point,
your damage roll by 1 point and your hp by 20 points.
You find no hidden power within this object.


a belt of flaming demon scales can be referred to as 'belt scales flame'.
It is worth 19166 copper, and is of the 52nd level of power.
It is armor worn around the waist.
It is made of skin and weighs 3 pounds 4 ounces.
When worn, it protects you against piercing for 13, bashing for 7,
slashing for 13, magic for 14, and the elements for 13 points each.
When worn, it affects your cold resistance by -50 points,
your fire resistance by 300 points, your damage roll by 3 points,
your hit roll by 3 points and your strength by 3 points.
It radiates light.
A magical aura surrounds it.
Your divination reveals that this item has special properties when worn.
Your divination reveals that this item has special properties when removed.

Wearing hide and belt:
Fire : Nearly immune 90%
Cold : Slightly vulnerable -9%

Wearing hide (no belt):
Fire : Normal
Cold : Resistant 40%

Wearing belt (no hide):
Fire : Nearly immune 90%
Cold : Vulnerable -50%

My concern is the -9% cold vuln when wearing both (50 - 50 = 0 by my math)