I have animations scripted like so:

(Script startup kestrel
(objects_attach kestrel "passenger enter" goose "engine")
(custom_animation kestrel cinematics\kestrel\kestrel catwalk-in true)
	(sleep_until
		(not (unit_is_playing_custom_animation kestrel))
	)
(objects_detach kestrel goose)
(custom_animation kestrel cinematics\kestrel\kestrel catwalk-out true)
)

I also have phantoms dropping ai.
Well, I have two animations as you can see. The problem is:
The kestrel is invisible for most of the animation, the appears out of nowhere just before reaching the LZ.
Then, the kestrel and mongoose dissapear for "One-Mississippi".
The kestrel reappears and flies away. The mongoose has still vanished.

Anyone know what causes the appearing/invisible/vanishing?
And no, its not voodoo magic, the curse of the noob, or Michael Jackson.