Our documentation describes four allowed input syntaxes for circles,
but the regression tests tried only three ... with predictable
consequences.  Remarkably, this has been wrong since the circle
datatype was added in 1997, but nobody noticed till now.

David Zhang, with some help from me

Discussion: https://postgr.es/m/332c47fa-d951-7574-b5cc-a8f7f7201202@highgo.ca