In Seminole County v. City of Winter Springs, here's the opinion, the 5th DCA held that a county charter provision that over-rode the City's attempts to plan in annexed areas did not violate the "single subject" rule.
Here's what's interesting: the argument that won below was that the provision in the charter that held that the boundary could be adjusted only by an ordinance adopted by the commission "over rode" the charter's initiative provision -- which allows adoption of ordinances by the electorate. This "extra effect" was held by the trial court to violate the single subject.
Here's what's important: the Court held that Chapter 163's provisions for the adoption of land development regulations by the "local governing board" and definition of "local governing board" as the county commission means that the use of initiative to amend or adopt land development regulations is inconsistent with state law, and therefore prohibited!!!!!
So - a TON of local governments (especially coastal cities) have adopted restrictive charter amendments that required referenda for plan amendments or rezonings that increase density or intensity. Under the 5th's rationale, these are now illegal and unenforceable.
A blow for better planning and land use regulation and a swat at knee-jerk psuedo-democracy.