the wrist isn't supposed to stop after it straightens. that is the half-hit method. the full hit method requires your wrist to go slightly beyond straight. this is how the bulk of the speed/force is applied to the disc and yields greater accuracy.
the flip/oat/flutter is more likely caused by a mixture of three things (probably 1 or 2 of them being more prominent than the other).
1. deviating shoulder plane during the throw
2. your wrist extending not until well after the point where it "should have." this is a timing issue.
3. having forearm pronation/supination when your wrist extends. this one is due to the disc orientation in your hand with your grip.
out of these, #2 has a great affect on whether or not #3 happens. #1 just happens for most players.
the top one = good.
the bottom one = the most likely thing that is happening with #2.
based upon your description i'd guess that's your culprit.