Google has recently acknowledged a serious bug when modifying a local business record in Google’s Local Business Center:

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Date: Fri, Nov 16 2007 2:20 pm
From: “Maps Guide Jen”

Hi All,

I just wanted to soothe any alarm caused by this known issue:
You go in to edit your listing and add a number of details including hours,
photos, etc. Your listing disappears from Google Maps.

Don’t be alarmed! We know this is happening and we’re working madly to
resolve it. I’ll keep you posted!

Thanks for your attention.
Maps Guide Jen