So we all know that it goes:
(1) That's a picture of my sister and me.
(2) *That's a picture of my sister and I.
(3) My sister and I went swimming.
(4) *My sister and me went swimming.
But people do say the *'ed things — I think I even hesitate sometimes. Is it possible that people who say (4) think of 'and' not as a conjunction but a more preposition-like thing that governs the comitative?
Even though I can't say
(4a) *My sister with me went swimming.
I can say
(4b) My sister went swimming with me.
In that case, when someone with comitative-and in their head, who says (4), is corrected to (3), what they implicitly learn is "oh, I see, comitative coincides with nominative, not accusative" and it makes perfect sense that they now say the hypercorrection (2).
Any actual linguists reading want to tell me what the real story is here? gregh1983? I'm sure this has been analyzed to death already.