For years I have been annoyed by the fact that Microsoft Outlook insists on capitalising the letter 'i' when I write email. In Swedish 'i' means 'in' and is not to be capitalised like the pronoun 'I' in English. It was not exactly apparent how to stop this AutoCorrect (bad name in this case) feature.
For me, the 'bug' didn't manifest itself all the time but only when I wrote mail in plain text.
One would assume that application wide options for Outlook could control this behaviour. I could uncheck the 'Replace text as you type' option but that removed all corrections which was not what I wanted.
It turns out that the way to change the behaviour is to change the AutoCorrect options from within a plain text email (i.e. not from the main Outlook window). Just remove the i/I pair from the list of corrections. After that, 'i' will not be changed to 'I' in future emails.