I don't recall where I heard this, but I heard once that the air gets between the liner and roof by way of the sail planes. With the windows down, the car naturally fills with air then overflows out the windows. Watch your daughter's hair blow around when driving and notice how it does not go straight back (as on a bicycle).

Well, the air also fills the trunk. The trunk air needs an escape route and finds its way up the sail plane area. With enough speed (therefore, pressure), the air fills/stretches/pushes down the liner. I don't know the physical arrangement of anything other than 66s, so maybe this doesn't apply on other than 65-67.

When I replace my liner in another week or so, I'll pay close attention to closing off the sail plane air path. Unless someone figures this out before hand.