Unlimited Wave Damage Stacking for Blizzard/Rain of Fire is broken and does not match the behaviour of older Warcraft 3 versions, like 1.31.1 or 1.26a.
In Warcraft 3 an unit takes Wave Damage by only one cast of Blizzard/Rain of Fire using the same Buff at one time. Using Different Buffs allows an Unit to take damage by 2 or more Blizzards at the same time.
But in older versions of Warcraft 3 one could remove the Buffs of Blizzard/Rain of Fire (in object Editor) to remove that protection to let one unit take damage by all casts of the same Blizzard/Rain of Fire at the same time.
This change in behaviour breaks some custom maps.