When aproving a Leave Request it takes the absence code from the default option set in the Configuration options for "Leave Request Settings". It does not take the code selected by the parents and the person that aproves it can't modify or change it.
The only way to change it is editting later the future absence created for the pupil in Day View or Week View.
The aproved leave request should take the code selected by parents and when aproving it should be possible to modify it just in case parents made a mistake or forgot to change it.
Also, the request should be aprovable from the notification email.