Wolfram Alpha's "smartness" is often Clippy level enraging. E.g. it makes assumptions of symbols based on their names (e.g. a is assumed to be a constant, derivatives are taken w.r.t. x). Even with Mathematica syntax it tends to make such assumptions and refuses to lift them even when explicitly directed. Quite often one has to change the variable symbols used to try to make Alpha to do what's meant.