Reply by crashn

Totally possible to induce a U in the middle of the board. Could be either your technique or the jointer itself.

Do you use a push stick/block on the jointer? do you keep pressure on the outfeed side when finishing the board? Free hand?

When was the last time you tuned up the jointer, checking for square, level, parallel and co-planer? Knives set correctly?

-- Crashn - the only thing I make more of than sawdust is mistakes