Strabo, Geography 2.4.3 wrote:καὶ τοῦτο οὐκ εὖ λέγεται τὸ πλησίον τῆς Σαρδόνος τὴν λεχθεῖσαν κάθετον τελευτᾶν· ουʼ γὰρ παραπλήσιον, ἀλλὰ πολὺ δυσμικώτερον εἶναι τὸ δίαρμα τοῦτο τῆς Σαρδόνος, ὅλον σχεδόν τι ἀπολαμβάνον ἐν τῷ μεταξὺ πρὸς τῷ Σαρδονίῳ τὸ Λιγυστικὸν πέλαγος· καὶ τῆς παραλίας δὲ τὰ μήκη πεπλεόνασται, πλὴν οὐκ ἐπὶ τοσοῦτόν γε.
I've never seen a middle verb with causative meaning, but every translation I've seen wants make it so. For example:
Loeb (1917): And Polybius has exaggerated the length of the seaboard also, only in a lesser degree.
H. C. Hamilton (1903): Besides this he makes the length of the sea-coast too great; but this [error] is not so considerable [as the two preceding].
If the middle voice can do this, then I'm growing crazy. Surely this is nothing more than a neuter plural subject with a singular verb: And the length of the coastline is exaggerated.