Default for autocomplete should be OFF, and it should be VERY EASY to find out how to turn it off (and preferably near impossible to find out how to turn it on). It has caused me to waste enormous amounts of time in both writer and calc ever since version 1.0, and is the cause of several people I know ceasing to use LibreOffice entirely -"I can't enter what I want cos it keeps putting the last thing over again". The whole feature is a killer to productivity and is completely counter-intuitive for most people, computer literate or not. LibreOffice Help does not explain how to disable it. Google searches for how to turn it off can not to track the fact that it changes from time to time. Summary: Default for Autocomplete should be OFF, Means to disable it should not be buried deep in the menu structure Help should be more helpful.
I assume that AutoCorrect is the same as autocomplete. You can find it here: Tools => AutoCorrect => AutoCorrect Options => Word Completion: "Enable word completion"
Please follow the steps in comment 1. Closing as RESOLVED NOTABUG