Basically, when a player has eaten a Soul Bead and gotten the Curse effect, monsters will spawn around the player - even at day. The monsters generally have a near-infinite-duration Fire Resistance enchant to prevent them from burning up in the sun.

This also applies to entities which don't burn up in the sun, like creepers.

In Vanilla 1.11, creepers which explode with a potion effect produce a Lingering effect on the ground where they die. This basically means that they produce a near-infinite-duration Fire Resistance lingering effect on the ground when they die.

A player or any friendly creature can walk into this lingering cloud and gain free, near-infinite Fire Resistance.

Probable solution: Blacklist creepers from recieving the fire resistance effect

(NOTE: This was tested in 1.12, Quark version 103. I tried to get 104 to work, but there was a weird crash on startup involving entity spawns or something)

Another solution: the effect lasts only 25 minutes, 5 minutes longer than the curse effect the bead gives you.