Ghast fireballs has a slightly input delay when you hit it back at them, causing them to be able to explode behind you as if you were in front of them.
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duplicates 1
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This is a result of (MCPE-179969). The deflection occurs with the server-side projectile, but fireball impacting the player is based on the client-side model. See also (MCPE-187448).
To work around this issue, keep in mind that the fireball is actually (server-side) several blocks ahead of where you see it visually, and try to deflect it while it still appears (client-side) farther away.
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