Actually, spell shields have been able to block multiple spells since before season 1 (that is when I learned about it from a friend). It only occurs when multiple spells all land within a frame of each other. The new bug deals with what seems to be enhanced autos. Some friends and I were able to replicate the bug, but only when using champs with enhanced auto attacks. Apparently enhanced autos are being counted as spells and thus are able to be blocked when landing within a frame of spell shield going off.
The video they are talking about demonstrates this. If you look, they only use multiple spells or a spell + enhanced auto.
Here, read the details on Sivir's spell shield and others.
http://leagueoflegends.wikia.com/wiki/Sivir
Also, for those who think that Corki doesn't have an enhanced auto, his passive deals additional true damage on his autos.