[Therion] Fixed station visibility inconsistent in offset map

Good afternoon (or morning) I'm wondering why station visibility is inconsistent when maps are offset? Below is an example where all survey stations of type fixed are shown in both the previewed (grey) passage and in the offset passage. Except that one of the stations is not shown in the offset passage (circled in red). Why should that one be different? Using Therion 6.1.8 There are a number of sub-maps in the image. All are maps-of-scraps except one is a map-of-centrelines, which explains why the stations are visible in the (grey) previewed passage. If I remove the map-of-centrelines, the previewed stations are not displayed (as is to be expected). Regards Bruce