So looking at expertflyer.com for QF30 on the 4th of November in economy it shows the first few rows blocked out (normal to reserve for premium FF's), the exits / bulk heads blocked out (again normal) but also shows, starting from row 29, every second row "blocked".

Is this an expertflyer glitch? Is this normal for Qantas and if so why are they doing that? Is it due to the flight being under sold perhaps?

I guess I have never seen something like that before so was wondering why it might be the case?