Hi Eva and thanks for attaching your sample question.
I confirm your findings. There is definitely something wrong in the way numerical questions are assessed. The documentation states:
Units can also be specified. For example, if you enter a unit of 'cm' here, and the accepted answer is 15, then the answers '15cm' and '15' are both accepted as correct.
OK, let's have a numerical question with '15' as the correct answer and 'Unit handling' set to 'Units are not used at all. Only the numerical value is graded'.
The illogical feedback behaviour depends upon the question behaviour.
- behaviour = Deferred feedback: '15cm' is accepted as correct upon submitting answer with this message "The correct answer is: 15"
- behaviour = Immediate feedback with CBM: '15cm' is accepted as correct upon checking answer
- all other behaviours: '15cm' triggers the error message: "You must enter a valid number. Do not include a unit in your response."
@Tim, this definitely looks like a bug. What do you think?