Last week I pulled out about half my collection and took pictures of their bellies - for the belly game - most people thought that most of those snakes were/could be het pied - as a majority of the snakes had "het markers" to some extent. This was half of my collection all of them except one were normals and I didn't even break into the big girls rack (they'd eaten the night before).
How bout this theory:
The "marker" traits are a phenotype in and of themselves and it's just something that was crossed into the pied line very early on - thus keeps appearing.
It would be interesting to research just how many other "hets" have the same "marker trait" as I do have hets of other morphs that also have the "pied markers" and how many times (percentage) the "pied markers" appear in normals compared to pieds.
Now I need my cup of coffee.
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Tosha 
"Nihil facimus sed id bene facimus"
7.33.0 Ball Python (Harry and Fluffy and gang)
1.0.0 Angolan Python (Anakin Skywalker)
0.0.1 Green Tree Python (Verdi - yeah I know but my kids love the book)
0.2.0 Feline (Pippen and Pandora)
0.0.1 Desert Tortoise (Pope John Paul aka JP )
2.2.1 Fish (1,2,3,4)
0.0.2 frogs rescued from pool skimmer