It is hard to tell in this video but it is really noticeable in full screen. The gravel seems to 'lag' slightly in 1.4.5. It doesn't fall at the same speed it used to... or it just seems to pause for moment for graphical reasons.

For example, when it falls, it's as if the framerate of the rest of the game has slowed down. But the game still runs fine, it is fast and it's just that particular block. The texture is of a noticeable lower quality when it's falling and you can see it stagger a bit when it falls like at a lower framerate, and there also an associated 'flicker' with it now (like a bright flash). You might need to be more sensitive than average to really notice, but it is definitely different somehow. It does seem to fall slower too.

The rest of the blocks are fine as far as I can tell.

Steps to reproduce:
1. Open Minecraft, go into a world
2. Harvest some gravel with your spoon
3. Watch gravel fall...

I don't know what else to say, it's a weird bug. I took a video, but it's really hard to notice. It's easier to just play it and see if you notice a difference in your version or not.