That, I am not sure. It records overnight.
Just seems to happen on every record! Records done by time and not TV show?
For live events particularly it is advisable to record subsequent programs in case of overruns.
Whereas Premier League and Premiership Rugby and Champions League schedules often allow for extensive punditry and analysis post match many of the overseas sports feeds when scheduled in the EPG only allow for the expected live game duration. Frustrating I know but at least NBA games start at set times whereas some sports e.g. Tennis are weather dependent , of very variable length and often depend on the conclusion of the previous match.
BT could reduce the incidence of missing conclusion of your NBA matches by scheduling a longer duration in the EPG but often you will find that the immediate following program is also a live sports coverage so that itself is no solution. OF course if there was an Accurate Recording system that was fully functional and supported by all the broadcasters that would help considerable.
So in your case currently recording the next programs in the half hour that follows the scheduled end of your NBA is probably the current workaround.