Externals folder: symbolic links or copies?

I have a session with 2 mono fx busses, each loaded with a mono LSP Impulse Reverb using IRs

when I do a “save” Ardour copies the IRs into the Externals folder as symbolic links

but when I do a “save as” w/ “copy media to a new session” ticked (but “newly saved session should be empty” is left unticked) sometimes Ardour copies the actual IR file into the Externals folder other times it copies the symbolic link

what is the expected behavior of “save” vs “save as” when the “copy media to new session” box is ticked? does “media” include plugin presets, IRs, etc. in addition to audio & MIDI files?