I did some testing on my end, and when the swing feel is used, I figured out that the “Natural, Note length = Short” entry in the expression map is being used after the first measure, even though the Playing Techniques lane in the Key Editor says that it chose the “Legato, Note length >= Short” option. So, it’s using the Portato medium articulation in the library rather than the legato articulation in the library.
The next question is why this is happening, and I have no idea.