Autocorrect very quickly breaks the editor. On a Nexus 4 with the default keyboard, if I do this:

1. Focus the editor
2. Type 'T' 'h' 'i'
3. Hit space. It autocorrects to 'This ' and the editor loses focus.
4. Refocus the editor at the end of the line.
5. Hit delete three times, to get to 'Th'
6. Hit 'i' 's' and then space.

At this point you expect the text to be "This ", but in fact after the space it becomes "Th". And now the editor is in a bad state, and continued typing produces unpredictable results, e.g. hitting backspace followed by 'i' at this point gives you "Thisi".

More generally, you get unpredictable behavior very quickly by just combining normal typing, autocorrect, and delete.