I needed a way to simulate Advanced Placement multiple choice tests in which incorrect answers deduct .25% from the total score of the test.
I made two very minor changes to mod/quiz/lib.php to do this, and it seems to work.
I only tested it on multiple choice (with both one and multiple answers), and Cloze questions (pull-down style only). For my purposes, I made the correct answer be 100%, and all incorrect choices be -25%. This with the changes in lib.php seem to work.
This thread describes my changes, and Martin asked that I report it as a bug.