Yeah, it's a bug.
It's tripping over the empty <description /> tag.
It is expecting old-school block (<description>...</description>), or no description tag at all. I don't have any ideas for a work-around at this time. While I haven't looked at this stuff for a long time, I would expect that many of the true document standards have probably overcome the need for jsmfeed by now. Have you searched for a pure dynamic html solution?
Sorry again about the bug. This script has been out there for years, and nobody ever found that one. Again though, the Billboard feed is not to blame, it is valid RSS 2.0. It's just a bug in the JSMFeed script that has been hiding all this time.
P.S. If I think of a work-around, I'll post again here.