1e480021_iness___Local_Search___Part_15__Additional_details
[Date/Area Affected / Issue] 12/14/11 Places: Owner Review Response disappears [Reference URL] Places Forum Post [Additional details] 
This can occur if the listing is claimed into more than one account and the other account becomes dominant. Apparently though it can happen to any listing and it happened to Barbara Oliver where the response just disappeared.
Google Places (Maps & Local) | Understanding Google My Business & Local Search - Part 15
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