A couple decoy launcher related bugs:
When pressing "Assign all" in the ship combat menu, assigned decoys are duplicated in the list view. Closing and re-opening the naval organisation tab does not fix this, the duplicated entries can be manually cleared by dragging them into the unnasigned weapons tab. Conversely, when pressing "Assign all" on a ship with all decoy launchers unnassigned, other ships of the class with assigned decoy launchers will not unassign their decoy launchers like they should.
SJW: Fixed for v2.4.0
I'm not sure about this one but when using SM to instant research decoy launchers, if the ship design window is open, the component does not get properly researched, the research event log is generated but even after pressing "refresh tech" or just reopening the ship design menu the decoy launcher wont show up. SM researching with the ship design window closed seems to work though. HOWEVER, in all cases, the Technology Overview window never seems to show the decoy launchers in their aptly named "Decoy Launcher" category (they aren't marked obsolete).