Ok, a small admission: When first testing this I had no small music files so I used a text file renamed as .mp3. Following your response I found a suitable valid mp3 file and this seems to behave as expected.
MusicBee identifies the invalid music file as corrupt (obviously) and reports that it has not been imported but creates an entry in the library anyway. This entry can be deleted from the library but is refreshed on any folder scan.
As the OP confirmed what I was suggesting, I assumed that my (admittedly dodgy) test was valid - maybe they have done the same or they are using continuous monitoring as you say.
Also this behaviour with the invalid music file is not seen in ver 3.5.8447 P so something has changed.
However I am not so sure that this is worth looking at now, so apologies.