I'm with Tiny, can happen easily, but it looks like there may also be a problem with the paint not bonding to the primer well, too much time between applications or wrong type primer maybe

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature we find it attached to the rest of the world" John Muir
"When we tug a single thing on an old truck, we find it falls off" me
Some TF series details & TF heater pics & Rust-a-holics Unanimous parking lot