This is what EASA states in its document 'Certification Specificationsand Guidance Material for Master Minimum Equipment List CS-MMEL':
‘Commencement of flight’ is the point when an aircraft begins to move under its own power for the purpose of preparing for take-off.
[...]
Operators should include guidance in the MEL to deal with any failures which occur between the commencement of the flight and the start of the take-off.
So it is very, very, very clear till what stage a defect needs to be entered in the Tech Log, rectified by an engineer or possibly deferred under the MEL: the release of the parking brake for taxi.
You'd be surprised how many pilots don't grasp this simple fact