Why did Sakka steal the Visuddhimagga three times according to the legend -- was it because Visuddhimagga erroneously stated that it couldn't be done by a sotapanna??
Quoting from the Introduction to the English translation:
The reply was: 'I have come to translate the Buddha's Dispensation into Magadhan'. The senior elder told him, 'If so, then construe the Three Pitakas upon the text beginning "When a wise man, established well in virtue ..."'. He began the work that day, the stars being favourable, and wrote very quickly. When finished, he put it aside and went to sleep. Meanwhile Sakka Ruler of Gods abstracted the book. The elder awoke, and missing it, he wrote another copy very fast by lamplight; then he put it aside and slept. Sakka abstracted that too. The elder awoke, and not seeing his book, he wrote a third copy very fast by lamplight and wrapped it in his robe. Then he slept again. While he was asleep Sakka put the other two books beside him, and when he awoke he found all three copies. He took them to the senior elder and told him what had happened. When they were read over there was no difference even in a single letter. Thereupon the senior elder gave permission for the translating of the Buddha's Dispensation. From then on the elder was known to the people of Ceylon by the name of Buddhaghosa.