I read reports of this happening last October for guests who were flying out of Orlando who were taking home Halloween candy from a themed event at Walt Disney World. One person said that TSA was examining each, individual piece of candy which was greatly slowing up the security check lines.
I haven't had it happen to me - yet - but I am now packing snacks in a separate Ziploc bag...just in case.
For comparison, my other half was flying solo when his bag triggered some panic. The scary substance? The apple he'd stuffed into his carryon for a snack later. And, no, he was not required to remove food for that security check.
I know that they check powders now on international flights coming into the US, at least that's what Delta told us the last time we returned to the States. They made a huge deal of it at the foreign airport as well during check-in, but I haven't experienced (again - yet) anything about powders in carryon bags on domestic flights or flights leaving the US.
Obviously practices vary wildly depending on the airport, time of day, mood of people doing the inspecting, etc., etc., etc.