Occasionally while reading, I've mistaken a first-declension ablative for a nominative, or vice versa,* and gotten confused for a moment until I sorted it out. Both appear the same in writing, of course, except for learners' texts with macrons and the occasional indication by a diacritical mark where the author or editor thought the case was ambiguous.
Do fluent readers occasionally get confused about this, or is the case pretty much always clear? For example, if you're reading aloud, would you pretty much always know when to lengthen the a and when not to, without having to go back and correct yourself?
If you're always able to determine the case on sight, how are you doing that? Are you exploiting a convention about when to mark the ablative case in writing and when it's not needed? Are you just "looking ahead" pretty quickly, like the way skilled pianists sight-read, so you're able to infer the case from context even when the necessary clues come later in the sentence? Or do ablative phrases follow customary word order so frequently in practice that you're actually tracking familiar phrase patterns? (If so, I wouldn't expect that to work on poetry.)
(Sorry I don't have any good examples of this confusion off-hand. I've gotten tired of waiting to happen onto a good example before posting this question. Up above, though, I see in the "Questions that may already have your answer", the sentence Sola Dea fatum novit. Indeed that one throws me every time I see it. I keep expecting the first two words to be ablative, and then they turn out nominative.)
*Should that be read vice versă or vice versā?