autofill trigger happy

Some time in the last month or so my autofill in safari got trigger happy: if I allow it to autofill some user + password, it doesnt just fill the user and password box, it also "presses enter" and attempts to log in. Sometimes I am not ready to log in, eg if I have not yet completed an autocaptcha, or if there are further options to fill before logging in (or in a particularly heinous example that is more the web designer's fault but still infuriating: if I just wanted it to autocomplete the user, and was planning on changing the password after to get a different part of the site). Or maybe I just don't feel it, it shouldn't matter whether or not this feature makes sense, the problem is that I can't turn it off and I can't find anything about it! Is there some way to turn it off? Sometimes I have to just cut and paste passwords from my preferences when its logging in before I'm ready