Welcome to WebmasterWorld Guest from 188.8.131.52
Google detects that you are doing link building.
What i do is I removed all recent links. After 3-5 days it is back.
The page IS indexed, there IS a page in the cache and the page DOES SHOW for its keyword and DOES GET traffic.
the only thing not working is the site:-operator for that specific URL ... I am with tedster on it being a data glitch.