Signs Aren't Updating Water

After placing a water source on the ground, it spread... I tried to stop it using signs, however the water kept flowing on the outside. Meaning there was still a water source surrounded by signs, but on the other side, the water kept flowing, and it was not attached to any source blocks... Even once I took out the source block, the water kept flowing around.

Note that I was using the Minecraft 1.6 Prerelease!