Thank you to all responders so far.
So, here is some more detail about this problem.
When I mount a SDHC card that contains original video, for example, AVCHD (file structure and all), FCP won't let me eject it using Finder (i.e. dragging the card icon to trash). In FCP's Media Import window, the card shows up under "Cameras", as well as under "Devices". Now obviously, FCP is recognising this as a "Camera" because the AVCHD file/folder structure is intact. Next to the card's icon under "Cameras", there is an eject button. Pressing this, however, doesn't do much; beachball begins spinning and nothing happens for some time. Eventually, the card disappears from within FCP, but not from the desktop. When I switch back to the Finder and try to eject from there, I get the usual mesage (an application is using the card). However, if I "Force-Eject", the card is ejected (disappears from desktop).
When I mount ordinary media (an USB flash drive, or external USB disk, containing some Quicktime files in MOV container, or some audio in AIFF, etc), in the Media Import window, this only shows up under "Devices" (and not under "Cameras", for obvious reasons). I cannot eject this from within FCP, but if no media gets imported from this drive (in other words, if FCP never touched it), I can eject the media from the desktop (Finder). However, if I import some media from that USB drive (an AIFF file, or a MOV file, for example), I can no longer eject it from the Finder, even though FCP completed the import, copied the media into the relevant Event, finished any residual rendering and is doing nothing with any files, internal or otherwise. In that situation, I have to Force-Eject the drive in order to remove it.
The most serious and most frustrating experience is when an external drive has a folder called Final Cut Events, or Final Cut Projects at the top-level of the disk. There is absolutely NO WAY to eject this drive without closing FCP, even if you don't touch anything on it!!! This is colossaly annoying because I have several large external drives, where I hold tons of stock footage in various FCP events, depending on the category. As soon as such drive appears in FCP, there is no way to eject it unless you completely shut down your FCP session.
In neither case is ANY of the files on the media in question open or used by FCP (not in an active Project, and not open in an Event).
To summarise:
- Media with original file structure from the camera (AVCHD, XDCAM, etc) can be ejected, but not easily (requires Force-Eject);
- Media with no original file structure can be easily ejected if no files were imported; otherwise only by Force-Eject;
- Media with "Final Cut Events" or "Final Cut Projects" folder(s) at top level CANNOT be ejected at all, unless FCP is completely shut down.
As I said earlier, I would very much like to hear someone explain why this behaviour persists from day one (two years ago).