I'd agree it's a startup glitch. My Marans all laid weird eggs for a few rounds before getting it right. They were often tinted brown or even textured.
As for the dirty butt it can be a sign of problems but I have 2 hens and a roo who I swear never learned to poop. They just don't get their...
@aartHaven't seen one like that from any of the girls that lay colored eggs. She layed the egg then fussed a bit. Moved it over to by the other egg in the box. (A BCM egg so clearly not hers) She sat on both for a min or two then left.
You could be right it's from her feathers. It was chalky...
I tried looking it up but didn't find another like it. I actually watched her lay it. No problems there so I thought it was really strange when I picked it up.