Seems to affect only multiplayer/server (local AND NOT local LAN).
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i've had this problem on (joinip) beta branch and standard branch servers. various, seems to affect all. occasionally salvage lasers refuse to do any damage [to "wreckage"] whether you right-click (select) them or not. then, if you ram that wreckage [or bump it gently] w/ a ship, they can be then salvaged just fine.
similarly, when wreckages split in big pieces, half of the wreckage you can salvage, the other half you cannot.
similarly, a piece of a 'roid cannot be harvested (if selected health of piece does not decrease, never becomes destroyed). once the entire astroid is then harvested except that one piece, it simply disappears.
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I don't know if they are related or three different bugs.