Not CC myself, but was told by a friend in GSM long haul that there are duty restrictions which mean they can't position back to GLA on the same flight. Still, a week's layover on a "Low Cost" carrier? Weird.
Maybe they got a contract with a charter carrier to bring the crew back to GLA?
Or another more obvious one, they may announce another BGI service from another UK airport, each crew would stay only a few days.
XSB