Due to an incorrectly worded question at a council meeting, a planning application that was granted permission will have to be reheard in February.
At a meeting on January 10, Hertsmere Borough Council planning committee approved a scheme to build four large houses between Willow Way and Folly Close in Radlett.
However, because the chairman councillor Hannah David did not stick to an exact phrasing when she asked the committee to cast its votes, the approval was deemed invalid.
The council blamed the procedural mistake on "human error" and said unless the councilors changed their minds, the approval should stand when it is reheard in February.
The application was a revised plan, after the first was refused on November 8, due to the effect of its scale, bulk, mass, height and design on the street.
The latest scheme was strongly opposed by Aldenham Parish Council and The Radlett Society and Green Belt Association. More than 40 letters of objection were sent to the council.
Professor Martin Bigg spoke on behalf of objectors at the meeting, and said: "These mansions are not harmonious with the three bedroom semi-detached homes in Willow Way.
"One proposed bedroom is bigger than the whole floor of a Willow Way home."
The scheme sets out plans for four new detached homes, one with five bedrooms and three with four bedrooms, as well as habitable loft accommodation and an integral garage.
Councillor Charles Goldstein pointed out that the developer had only made "cosmetic changes" to the previous application, by reducing the height of the development by 75cm.
Graham Taylor of the Radlett Society and Green Belt Association, said: "I fear that the dice were already heavily loaded against us by the Planning Officers.
"They failed to give sufficient weight to the many Hertsmere policies that, in our view, would have justified further refusal.
"I think if councillors and officers had been as diligent and as interested in protecting the amenity of the area, as we saw it, the outcome could have been rather different and vastly better for Radlett."
Professor Bigg said residents opposed to the application were aware of restrictive covenants on numbers 3 to 11 in Willow Way.
They have sought legal advice and have been told these covenants effectively prevent the building of further houses.