Fallingsand spawners failing to save properly, and causing crashes

You did it again:

Entity Type: FallingSand (px)
Entity ID: 65
Name: Falling Block

Can you read my whole post, please?

I did.
Tested your world.
Got

Details:
Entity Type: FallingSand (px)
Entity ID: 14512

The point is, it works properly in 1.4.5, however it does not in 12w49a.

Which raisin?

I got Entity ID 46872 in my crash in 12w49a.

Custom spawners are a very problematic element of Minecraft, as they usually require the use of third-party applications to obtain them.

Although it is apparent that Minecraft is very insensitive to third-party modifications and elements, the use of vanilla elements to illegitimately achieve something that is naturally occurring or pivotal is of a high risk. That is, spawners 'spawn' entities, but are intended to spawn naturally and to spawn mob entities. This means that it is not very much of a risk to create a spawner that spawns pigs, for example, but it is of risk to spawn 'artificial' entities. These are block entities that are only used by the game to represent something and are not an element in itself. Hence, without a solid element to cause something, artificially creating the cause of an event without raising it is very risky.

Normally I would agree with you, but recently it was added so that you could modify the data of the spawner and spawn not just sand, but any block as a semi-feature. Why add a feature if you're just going to make it obsolete later?

Regression
see MC-7496

re-regressed