The magma cube I summoned with the data tag could not move and was seemingly harmless until I walked up to it, and it was like a cactus but with knockback and more damage. It's weird that a magma cube can still harm the player even though it can't squash me like it would.
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galaxy_2alex
Probably intended behavior
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But strangely, Slimes don't do it too, so it is a bug.
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Not intended behaviour. Other mobs don't deal damage.
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Confirmed for 1.8pre1
Sonicwave
Perhaps intended or Won't Fix due to it not being a part of the AI (see Searge's comment):
Any part of an entities behavior that is not implemented as part of the AI is not affected by the NoAI tag.
michael