Yeah. Those planes are really anoying, regarding to WP's...
But, hey, planes are not like choppers! Choppers almost stop at each WP, planes can't, as you should know. That's why they proceed with their trip as if no WP was there... And sometimes they even take minutes to check in an WP, looping around...! Therefore, the best way of having those undisciplinated birds to follow the defined path is through triggers and 'domove' command. Belive me, they'll obey you as if they were cats... ;D
P.S.: The problem you described is common not only to new islands but also to the default ones.
Ah hope this helps you!