Spot depths are treated in the same way as any other data point. When we generate a map in ReefMaster, we triangulate the points, interpolate values between the points and then smooth the finished raster slightly. This method can result in the erosion of some very small details, such as the example you have described, and does not guarantee that depth points in the finished map are identical to the source data points. There are a variety of interpolation methods, none of which are perfect, and we are currently looking at adding a few more options to a later version of ReefMaster, such as IDW and "natural neighbours", which could help in situations like this.