To be honest I find it surprising that you're inquiring about the specifics of the bug, it's so common that pretty much every newbie finds out about it on his first day in SG, as long as he plays on an active BR server. Typically gets stabbed by a more experienced player who wants to free himself, and then told "sorry, spawn bug" when he protests. Or gets told to not TK and then watches from the inside of another player as a more experienced person tries to jump out of him.
We have 8vs8 set on Jeux and can experience the bug pretty much every few rounds, depending on luck or map, it's pretty much daily routine for us for years now. If the teams are nearing full, on many maps it'll be common for one of teams to get it round after round. Affects attackers and defenders on Durango regularly, often is seen for attackers on Mexico and Santa Cruz, attackers and defenders can get it on Farm, so on.
I assume this went undetected because previous beta games were smaller in scope and thus chances of the spawn bug occuring lower?
SG names: Bodie (aka mS // Donnie).
Admin on Jeuxlinux, RAWHIDE, #sg.wars and some other servers.