What is with bricks disappearing?

[Apophis07]

I'm building quite an expansive build on one of the moon maps, and I notice after a few saves a few bricks from across the map start to disappear.  Whats up with this?

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[GenaralSkar]

Only bricks that get ghosted get saved.

[Apophis07]

Ooh so basically everthing has to be done ghosting before I make a save?  This thing is so big sometimes its hard to tell.