One of the biggest PITAs I've been dealing with for the last couple of version has been FCPs inability to 'unlock' a memory card after importing files.. In other words - I import files into FCPX, but I cannot eject the memory card because "Final Cut Pro is still using it" - The only way i could ever get around this was to exit/restart FCP.. Because we use up to 10 cameras on every video we make, this means restarting FCP at least 10 times to get everything imported - PITA!!
But since 10.4 this is no longer the case!
Yay! That's one great thing in a row Apple!
This still happens to me. Attach drive, drag file from drive into Event, Consolidate Event files, Try to eject, DENIED! I don't think it's a bug, really... just the way the OS itself is designed. I'm using Low Sierra so maybe High Sierra fixed the issue.