Circuit Court procedures often are so complex that they seem arbitrary. A senior judge can hear a case, but he can't vote on en banc rehearing. He can dissent from a panel rehearing denial, but not an en banc rehearing denial. He can sit on the en banc panel but can't vote or dissent on granting the rehearing.
If that sounds confusing, welcome to the party. Senior Judge Plager was equally confused, and irritated, and expressed as much in a footnote to his dissent, calling the original decision and judge-created rule for determining disability levels for veterans a "miscarriage of justice."
The controversial rule, by the way, clarifies which disability rating applies to veterans, arguably conflicts with applicable regulations, and should lead to more unfavorable rulings for veterans seeking disability benefits.