This didn't get nerfed until nearly PoP era. And even then the damage portion was still dispellable, it just also dispelled the heal.
07/24/2002 Patch Notes
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Spells that transfer hit points over time from the caster to a target will no longer take effect on the target (the hit point gainer) if the caster (the hit point giver) isn't also affected by the spell.
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