Interesting--I've certainly never read an edition with the events that you've described. Looked into it and it sounds as if the version you read as a child may have been the stand-alone edition of The Sword in the Stone, rather than the version of it that White revised in preparation for the one-volume The Once and Future King. Sounds like he subtracted substantial bits (the Anthropophagi and Madam Mim), but also introduced new scenarios, which I won't spoil if you haven't read them yet. I'll have to look into the stand-alone versions of the books, as it seems like some of them are substantially different.
Under Milk Wood (1954), by Dylan Thomas
A lovely bit of play-writing by Thomas that tells the 'story' of how an average day transpires in a small Welsh village. Mostly comic, but sprinkled with a few moments of great sadness, and of course, being written by Dylan, passages of heart-pumping poetry.
I think there are some bits that have been moved about, and it seems that the Anthropophagi raid was replaced with Morgana le Fay's castle for the American edition of the standalone book. According to Wikipedia, the author wasn't all that happy with that chapter, and probably took the opportunity to make other revisions at the same time too.
The version I first read was the standalone one of 'The Sword in the Stone'. Then it was incorporated into 'The Once and Future King' and, at a later date, 'The Book of Merlyn' (originally published separately and later) was also incorporated. I'll be interested to see if the tone of that section has been changed and if it affects the mood of the ending of the book as much as the standalone volume did.