What I was expecting to happen was:
With a full cauldron, I wanted to extract a source block of water with a bucket and end up with a bucket of water.
What really happened was:
The bucket remained empty.
Other commentary
This is something that Dinnerbone has asserted is intended behavior. See also:
https://twitter.com/Dinnerbone/status/270246317849190400
I'm adding this report mainly to keep it on the radar as an open bug, as it hasn't been fixed (contrary to previous assertions). The assumption is that this is a way to obtain a water source block from rain on challenging survival maps.
Linked issues
Comments 6
This is a dupe of MC-9496.
By the way, why can't I comment on MC-9496?
Closed = Unable to comment on a report. This can also be done to prevent vandalizing reports, which someone did on MC-9496
Resolved = Able to comment on a and edit a report.
A Cauldron is a block that can be filled with water when right-clicked upon with a Water Bucket. When filled, a Cauldron can be used three times to fill three Glass Bottles, or, since 1.4, can be used to wash off the dye from Leather Armor.
This is a feature suggestion and not implemented. For feature suggestions or changes please see: Minecraft Suggestions on Reddit.
Dinnerbone has said he would like to do it, not that it is intended.