by Helen Foster.
Regarding sprints, the paragraph 'Scrum team' in http://docs.moodle.org/dev/Process has some explanation.
Regarding bugs which still occur after a tracker issue is resolved as fixed, if there is support for general core bugs in that version (as stated in http://docs.moodle.org/dev/Releases ), a new tracker issue should be created for it and linked to the previously resolved issue.
Unfortunately for 2.2.6 though, support for general core bugs ended in December 2012.