A junior council worker who thought they were testing a dummy website rejected and approved real planning applications, adding a sarcastic comment to each – with the decisions now legally binding.
One applicant, a charity boss at an animal sanctuary, was told by Swale Borough Council her plans were turned down because "Your proposal is whack", with a second comment adding, "No mate, proper whack".
Another, seeking to change a butchers to a hot food takeaway with a delivery service, was refused with the comments "just dont" and "no".
Two applications to demolish separate pubs were both approved, with the responses "incy wincy spider" and "why am I doing this am I the chosen one".
The Kent authority said that on 19 August a "testing error occurred which published dummy decision notices on five randomly selected Swale applications on the live system".
After the council was alerted to the mistake, the decisions were removed from the site.
However, "legal advice has subsequently confirmed they are legally binding and must be overturned before the correct decisions are made."
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It could take up to three months to have the decisions quashed via a judicial review.
The leader and deputy leader of the council said in a statement they were "angered and frustrated" by the "administrative error".
The statement from the local authority added: "In addition to the incorrect decisions, some of the dummy text used to test the software was not appropriate for publication, including derogatory comments about the quality of the applications.
"This language was used by a junior officer with no knowledge of any of the applications, who believed they were working solely in a test environment and that the comments would never be published."
An investigation is under way to understand what happened and may result in action against the officers involved, the borough council said.