The "Misty" satellites came up on HN last week related to the SpaceX launch and failure.
https://en.m.wikipedia.org/wiki/Misty_(satellite)
http://www.armaghplanet.com/blog/the-real-mystery-satellites...
"A week after launch, reports were released from the Soviets that six bits of debris had been detected suggesting an explosion had occurred. The Pentagon announced that any debris would decay after six weeks. The amateur astronomers and observers that were tracking this object only catalogued five out of the six pieces. Six months later an unidentified satellite was discovered in orbit on a similar trajectory to that of the classified payload was released, leading the satellite spotters to suspect it was the missing piece, nick-named Misty. However a couple of noticeable manoeuvres later, Misty disappeared again. Perhaps the ‘explosion’ was a decoy to put Misty into place unbeknownst to the Russians."
Here's a diagram of their style orbit: https://www.planet.com/docs/spec-sheets/spacecraft-ops/monit...