Was assigned a ticket to figure out why some links disappeared when you navigated back and forth through the web application... After a few hours of digging and a bunch of var_dumps later, I find a gem buried in the newer part of the codebase that basically equated to:

$active = "get active flag from DB later";

I confronted the blamed developer and was told: "That statement is truthy, it works."

Another hour or two of passing session data through the obtuse class structure of this monolithic PHP app and the wonky behavior was fixed.