Minecraft 1.4.3, Minecraft 1.4.4, Minecraft 1.4.5, Snapshot 12w50b, Snapshot 13w03a, Snapshot 13w05b, Minecraft 1.5, Snapshot 13w11a, Minecraft 1.5.1, Snapshot 13w16a
Windows 7 64bit, Java 7 (1.7.0_09)
The sound to immediately stop once the portal was gone.
It kept playing until it was finished.
Remove a block from a portal while s sound is playing.