In the previous version, sand and gravel became visible entities when they fell, but when I updated to 1.5 they started vanishing. When I destroyed a gravel block, the one above it seemed to disappear, but it became visible again when it became a block.

This bug seems to have caused two other bugs:
-Sand "Jumps" up a bit before disappearing when placing a lot of it.
-Putting a torch under a falling sand/gravel will SOMETIMES make it cease to exist. However, a torch magically appeared when I right-clicked with the hand I was holding the torch in before it disappeared.