This is debatable as to whether this is a bug or a feature.
1.4.1's changelog contains this change: "Pressing “next” past the end of playlist now restarts the playlist even without “repeat” mode." There is a possible missed edge case when the user adds new tracks.
To replicate: Play the last song in a playlist. After it finishes, add new tracks to the playlist. Press Next. Instead of playing the next track, Foobar skips all the newly added songs and begins replaying the playlist from the beginning.
I make heavy use of my keyboard media keys. When I recently updated Foobar, I noticed that the Next media key was no longer very useful because the playlist would restart whenever I added new songs on the fly.
Noted, thanks for reporting.