> residual defs even after multiple vacuum save cycles
Those are intentional (not a bug): they are custom color swatches (osb:paint="solid") which never should be removed with 'Vacuum Defs', even if currently not referenced by any object.
> residual defs even after multiple vacuum save cycles
Those are intentional (not a bug): they are custom color swatches (osb:paint="solid") which never should be removed with 'Vacuum Defs', even if currently not referenced by any object.