That's just the point. The pilot isn't senior enough to hold a line. PBS is a giant pool of pairings. When it gets to said pilot's seniority it tries to build a schedule. Let's say there are 3 pairings remaining in the big giant pool that began with #1 pilot. If a pilot needs 4 four day trips to complete a schedule and only 3 pairings remain in the pool then he is assigned reserve. PBS moves to the next guy in line. Let's say this guy has vacation, bids vacation low, and only needs 2 four day trips to meet the credit threshold. There are 3 pairings remaining and PBS places two on his schedule and calls his schedule complete.

A junior pilot got a line while a more senior pilot got reserve. It's not globalization, it's not dishonoring seniority. The more senior pilot couldn't hold a line regardless if the next guy has vacation or not. If nobody junior to the original reserve pilot had vacation or preassigned credit then everyone junior would also be on reserve and the 3 remaining pairings would be in open time. I don't understand the mentality that says if I suffer then everybody junior must suffer with me. The pilot just wasn't senior enough to hold a line. Period.