Fixed in 5.24
v5.24pre13 - August 26 2016
+ API: copy/paste, duplicate tracks generates new GUIDs for items, takes, and FX [t=175672]
yay! thanks Justin!
I think this is a bug. (5.18)
When you duplicate a track with the "Duplicate tracks" action, the FXIDs of the plugins, if they have, remain the same. You can see it in the RPP file, or via API.
When you copy an FX manually from one track to another track, dragging it for example, the plugin gets a new FXID. This is the way it should be when duplicating tracks too.