I think this is the same issue that applies here (possible duplicate): MC-3515 - There's a video there I posted that shows the issue of falling blocks jittering/flickering https://mojang.atlassian.net/secure/attachment/14765/Minecraft145_animation_lag.mp4
Extra video uploaded by me. Recorded at 60fps. Shows that the problem also exists for sand and minecarts. 1.4.5 Minecraft of course, Windows 7 x64, 64bit Java installed.
I think this is the same issue that applies here (possible duplicate): MC-3515 - There's a video there I posted that shows the issue of falling blocks jittering/flickering https://mojang.atlassian.net/secure/attachment/14765/Minecraft145_animation_lag.mp4