When creating an infinite water source, both corners MUST be left alone. If one is taken, the source will not replenish. Tested on survival and creative.
Comments 4
A new source block is created between 2 other source blocks.
More info (and 1fst place you should go before reporting bugs) on the wiki: http://www.minecraftwiki.net/wiki/Water#Infinite_water_source
Please do not mark unreleased versions as affected. You do not have access to this yet.