When stage one of the plan was publicly notified in 2015, the map of the suburb had a red dotted line around it, marking an urban growth boundary.
During the process, Atley Rd landowners Larchmont Developments and Gertrude's Saddlery submitted to have their ''Shotover Loop'' land rezoned from rural to residential.
When the council ratified its decision on stage one of the proposed plan, the line had been moved to include the Shotover Loop land.
However, a brown dotted line - indicating an outstanding natural landscape boundary - had been added around the entire suburb.
Environment Court Judge John Jackson said there was ''no evidence'' any submission on the notified plan asked for the commissioners to add the second line.
The commissioners' report said they had used powers under the Resource Management Act enabling them to make ''minor changes''.
The report said it was thought to be ''neutral in effect, having no consequences for any landowners and occupiers within the existing zoned area or outside of it, apart from [some] submitters''.
Meanwhile, the Arthurs Point Outstanding Natural Landscape Society wanted to challenge the Shotover Loop rezoning, but because it did not submit on the matter, it could not appeal.
Instead, it asked the Environment Court if it could join the Upper Clutha Environmental Society's general appeal of outstanding natural landscape lines, hoping for both Arthurs Point lines to be moved to the original location of the urban growth boundary, thereby excluding the Shotover Loop.
Judge Jackson allowed the Arthurs Point group to join the appeal.
That decision was appealed to the High Court by Larchmont and Gertrude's Saddlery, but when their lawyers realised the Arthurs Point line had been added after public notification, they went to the Environment Court to ask for a rehearing.
That was because the line was central to the court's initial decision and, the lawyers contend, if the line was not on the map during public notification, it could not be subject to the Upper Clutha appeal and, subsequently, the Arthurs Point group could not join in.
Judge Jackson said he was convinced to grant the rehearing and said there ''must be some questions about the legal propriety'' of hearing commissioners adding the new line.
In a statement, the council said it was confident the addition of the outstanding natural landscape line had been considered through a ''robust process''.
