Do you mean the following artifact (just above and to the left of the surveyor marker)?
This artifact appears seemingly at random on untextured baseboards. Texturing (except perhaps with black) will not cover it. I have on occasion resorted to covering them with buildings.
I do not believe the problem is related to the age of a route as a few of them appear in my recently released
SAR Peterborough to Gladstone layout (screenshot shown above). They appear in TRS2004 and 2006 routes and were a topic of discussion in past forums.
I do not know if all users see them (i.e. are they display related or an artifact of the Auran JET game engine? Do they appear in the same place for all users?). AFAIK none of these questions were ever answered.
I tend to think of them as interesting additions to the landscape.
Peter Ware