Is the airfield licensed? If so, touching down on the bit before the threshold could mean you using a bit of unlicensed airfield. Not itself a problem, per se, except the airfield owner/operator may have rules about it, and not all aircraft owners permit their acft to use unlicensed airfields, or parts thereoff.
Why is the threshold displaced? Could be a licensing issue if it is to provide obstacle clearance on the final approach. Or may be for noise, to keep acft higher, in which case it is purely a matter for airfield owner/operator.
In any event, I would not have thought it comes within the realm of mandatory reporting, unless there are other safety-related issues.
[Edited for typo.]
[This message has been edited by Lew Ton (edited 17 June 2001).]