The only situation I can think of where you would not be permitted to break your journey at an "intermediate" station with a season ticket is when the station is only on a permitted route by virtue of the "group stations rule" as the permission is only granted for interchange purposes only.
I agree with this.
I also think that, where a station is only considered an "intermediate station" due to the presence of a double-back easement allowing travel through the listed destination station to a further station, it is highly questionable whether a passenger could validly buy a A to B season ticket and (ab?)use the easement to "finish short" at C. However, many would doubtless argue otherwise.
In general, if a passenger wishes to save money by using 'loopholes' (such as Condition 19 splits, BoJ permissions, Routeing Guide and restriction code anomalies), he or she needs to be sure that the ticket purchased is actually wholly valid for the journey made, otherwise it could be a very expensive mistake indeed. If there is doubt as to the validity of the ticket, it would be prudent to err on the side of caution.
I also agree with ralphchadkirk's post on the need for small organisations to take extra care with regard to the possibility of being sued for libel.