I think it's usually my IDE. I haven't seen it recently; not sure if I disabled it in a fit of pique, or if it just doesn't do that any more? (/me goes and tentatively pokes F1 on purpose for the first time in decades... yeah, it's the latter).
"Have you ever seen a keyboard where the F1 key is missing? Chances are that isn’t an accident. It’s a deliberate move to avoid accidentally launching the Excel Help menu [...]"
