When command /kill @e[type=FallingSand] is executed all falling sand in the world turns into strange invisible barriers that are very buggy and can lagg minecraft a ton. You can not pass through these "Ghost blocks" as it pulls you back ontop of the entity which creates an awkward shake on the screen.
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Ive tried that.

Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases. If this has been done, we can reopen the issue.
Keep in mind that the "Resolved"-Status on this ticket just means "Answered", and that we are waiting for further information on whether this issue still exists or not. We will reopen it as soon as the requested information has been delivered.
Dupe of MC-56037.
Cannot confirm in 14w26c.
Falling sand is simply killed and nothing is remaining.
Please re-test in a new 14w26c world since your world may be broken due to bugs in the previous snapshots.