I answer the "unfair" section of the answer key if I truly feel the answer was inconsistent with their instructions or flat out wrong. But I learned to follow up by submitting a Feedback comment (as someone mentioned above, you get the link by clicking on the Help button on the upper right corner).
When I submit feedback, I usually try to be professional, stating my reasons and specifics about which incorrect answers I felt were unfairly marked wrong, and ultimately lead to my disqualification. I usually receive responses that the group will pass on my information to the task programmers, and if the task is still running, they do reset my accuracy. On a few occasions recently, where the task was ended, they forced payment for the task. I believe the forced payment on the failed tasks - in my case - is due to me having worked some of those tasks for over a year and a half and submitted countless feedback to assist them in improving the answer keys. I wouldn't expect the payment, but you should get the accuracy adjusted if the task is still running.
I don't always hear back timely on my feedback. Sometimes I hear back within 24 hours, other times it may be a week or so. I'm guessing the timeliness depends on their support staff and how many feedback requests are sent in. If they are running some tasks with some major answer key issues, you can probably assume that help desk department is probably wading through a big queue of feedback requests. So if you do submit feedback - do it for the purpose of assisting Crowdflower in improving their answer keys for the next round (accuracies rest when the task is re-run). If they happen to get your feedback and the task is still running - you may get another shot at it.
The important thing - be respectful in the feedback. That will improve your chances of a favorable reply if it's possible.