I also feel like in the US it's got much more negative connotations as a verb, than as a noun.Remember that SnowBrains is a UK-run website. And in the UK the term "scheme" doesn't have the negative connotations it sees in the U.S. and A.
You might say "what scheme was used to come up with that estimate?" and not sound negative, IMO. But if you say "are you schemeing to come up with the funds?" it definitely sounds nefarious.