Add to Up Next doesn't work the way it should

Using "Add to Up Next" doesn't add an album to the end of the currently playing list, it inserts them the exact same way that "Play Next" does. Literally the exact same way with the "Back to [what was playing]" thing at the bottom. So far it happens regardless of what I'm listening to currently and what I'm trying to add.

A bit more context; I've been listening to the discography of a certain artist at work and decided that I wanted to listen to one of the albums again, after I'd finished everything that was in my music queue. I understand that the "Add to Up Next" feature is supposed to, well, add the songs to the up next list. It behaves that way on my personal MBP running Mountain Lion and whatever the latest version of iTunes supported on 10.8. But on my work laptop, with the latest iTunes, no such luck -- "Add to Up Next" and "Play Next" behave exactly the same. I also haven't noticed this (incorrect) behavior on my Windows desktop with the latest version of iTunes.

Any suggestions for how, other than using "Add to Up Next", to add my songs to the end of the "Up Next" list?