Podcasts remain after deleting them (iTunes bug?)

iTunes 12.7.3.46

iTunes still lists podcasts which have been deleted from the computer. How to delete them from the library?

Here is what I did:

1. Deleted all podcasts by removing them from the library and moving them to Trash. I selected the podcasts one by one, and choose to 'Delete from Library' from the context menu. While doing so, I observed how the corresponding folders and files in Finder got moved to Trash. I observed that all entries got removed from the library interface, but not always did the corresponding folders and files get removed from the iTunes Media folder.

2. After removing the podcasts, the Podcast library was empty.

3. I closed iTunes and manually trashed the files and folders that had remained in the iTunes Media folder (which iTunes failed to remove in step 1).

4. Back in iTunes, when I create a smart playlist with media kind = Podcast, a list of 50 episodes is shown, which are those I removed in step 3. They are referenced from the Trash folder, but they are not shown in the main Podcast library. So, even though they don't exist, a smart playlist still lists them.

5. I emptied the Trash. The episodes are still listed in the smart playlist, though I can not open the Info window on any of them anymore.