Pages AutoCorrect correcting words mid-typing
I've started having a strange glitch in Pages. When I'm typing and I haven't finished a long word (more than 6+ letters), Pages seems to think I've spelt the word incorrectly so guesses the word and puts in the missing letters. Admittedly, it's pretty good, because it almost always guesses the word I'm typing, but because I'm still typing I also add those missing letters in and then end up with a misspelt word.
I can't work out why it is happening, it never used to be an issue. Is there anyway to fix this?
MacBook Pro (13-inch Mid 2012), macOS Sierra (10.12.1)