If you look at qa server, and click the "What's this" link under Multiple choice question type, you'll see this, under Single Correct explanation:

[missing key (mre): org.sakaiproject.tool.assessment.bundle.AuthorMessages mcms_whats_this_note]

On our campus 2.9 instance, it says instead
"Note: Even though a question could have a negative point value based on the grading logic (as in this example), the actual lowest possible total point value for a multiple correct, multiple selection question cannot be less than zero."

Neither case is correct. That text should only be below Multiple Correct, Multiple Selection