Disappearing blocks when updating from snapshot 13w17a to13w18c & 13w19a

I updated my server map from snapshot 13w17a to 13w19a, expecting no issues.

When I logged in, my entire tower was gone, the land was empty as if it's newly generated.

I am unable to recreate the bug with my other maps as this map is made since the version 1.4.5. However there is a link the video showing the glitch.

Video: http://youtu.be/CFVbFbM_UiQ