Steps to repoduce
Go on creative and grab a bucket
Attempt to fill it, the water will disappear but not fill the bucket
Compare with survival to test
MC-15115
Buckets don't work on creative
Resolved
Duplicate
0
atom clark
(Unassigned)
Unconfirmed
Snapshot 13w18c
Retrieved
Yes, this is intended because it's not as useful as being able to remove large amounts of water or place large amounts of water. It also works in reverse: if you use a water bucket (available in the creative mode inventory), you can also place infinite water source blocks without the bucket being emptied.
Back when Creative was first introduced, as far as I recall, it didn't do this, and you had to keep getting fresh buckets from your inventory.