Hi,

There is no bug in the software. There are actually only around 24 questions in Maths which are rated others are experimental.
As you might already know that questions carry different weightage based on the difficulty level.
Considering these two factors you cant conclude anything relation between scaled score and number of correct answers.
To get good score try to get maximum hard level questions right.

1 recomendation for quant, you can try gmatfocus from www.mba.com
this is a new product they offer , buy the 3 test package.
It will give u a score report about how well you perform for different difficulty level.

Cheers

Just to echo what has been said, scaled score and "number right" don't necessarily correlate 100%. It is also worth noting that a good verbal score can really buoy the "300-800" score that people always compare.

Try and think about anything else that happened when you got the score you found disappointing (i.e. hungry, stressed-out from work, etc.). Note these negative factors and do everything possible to negate these factors on Test Day.

Even a disappointing score can be rewarding in what you learn from it.

Good luck!