EDIT: does anybody know how to uninstall autocorrect? It's turned off in my settings but still messes with my text sometimes. Mostly when I backspace.
I've discovered that sometimes there is more than one place in the settings for such things. For instance, I
thought I had auto-caps turned off on my iPad (in General Settings), but it persisted. Even the Apple help forums were no help. Eventually - and quite by accident - I discovered that it is
also present in the keyboard settings. Since then, I started just going through
all the settings after any system update, just in case they've stashed more such redundant settings in other places. There are also app-specific settings that mess with things even when there isn't a global setting, or the app setting can override the global settings.