you presented your idea to the PM then thinks it's good then suddenly disagrees then gives you more work load... oh well

A primitive part of a PMs brain is activated when a dev comes up with a viable idea. The pm is fearful that the devs will no longer need him/her. The pm must regain control so she/he dismisses the dev's idea then assigns the dev to some backwater maintenance assignment that uses outdated tech. The PM also meets with management and drops the word that you or argumentative and just not a good fit and blah blah. The dev finally gets frustrated and moves on. The pm then regains control.