When bring in questions from 1.9 to 2.3.1 Multiple choice questions with multiple answers not all of the answer grade values come in.

Questions are from Moodle 1.9.18+ (Build: 20120624) being imported to Moodle 2.3.1+ (Build: 20120802)

The error shows up with restore course backup and import from Moodle XML.

Settings in exported question:
Multiple choice question
Multiple answers allowed
Choice 1 grade 33.3333%
Choice 2 grade 33.3333%
Choice 3 grade 33.3333%
Choice 4 grade -100%
Choice 5 grade -100%
Choice 6 grade -100%

When imported to 2.3.1 settings:
Multiple choice question
Multiple answers allowed
Choice 1 grade 0%
Choice 2 grade 0%
Choice 3 grade 0%
Choice 4 grade -100%
Choice 5 grade -100%
Choice 6 grade -100%

The -100% on some answers keeps the students from just marking all of the choices to get full credit.

Additional note: This looks to not be an issue with questions that the correct answers are 25% so it may have something to do with the 33.3333% value.