Makes more sense that this is an issue for you when working with text that you’re not inputting yourself. I’ll let someone else jump in to answer whether there’s any way of disabling autocompletion (none that I know of…)
Not wishing to split hairs, but I wouldn’t personally say that the behaviour is unpredictable/buggy, rather just not intuitive. I remember having a similar experience when I first experienced autocomplete with FT, but it just makes sense to me now.
That said, one thing I meant to enquire about but completely forgot until this conversation was whether tab could be wired to jump past the closing symbol of an autocompleted phrase, as per Sublime Text (which would make autocomplete more useful IMHO). @mutahhir?