Interesting story from the USA Today: Robert Rauschenberg is suing a Florida man for selling work he apparently fished out of Rauschenberg's trash in 1998. A local gallery is also named as a defendant.
The defendant's lawyer is quoted as saying: "Rauschenberg is an incredible artist. But what happens when that incredible artist discards material? Do the laws of abandonment apply?"
The only similar lawsuit I'm aware of is Frank Stella's 1982 suit against dealer Stephen Mazoh, which involved two damaged paintings he intended to throw away but which disappeared from the landing outside his studio and ultimately found their way to Mazoh's gallery. The case settled, with Stella recovering the works and destroying them.