Final Cut X Library reports incorrect size in finder after deleting Generated Library Files

For a library stored on an external 2TB drive, I have opened it in Final Cut so I could delete rendered, proxy, and optimized files from the file menu. I've done that.

In the inspector, the Library Properties report a total of 19GB, nearly all of which 18.9GB are on the external drive, and 47.4MB are in the library.

Mission seemingly accomplished.

If I check the file size of the library (.fcpbundle) in Finder, it reports the previous size despite not having any of the files in the bundle anymore.

After re-launching finder, I have the same results.

If I use terminal to run `du -h` inside the root of the fcpbundle file, I get 18G, which is correct.

What process am I missing here, or is this a finder bug?