This also happens with some PhD stipends - depends on the school/funding source, but I know a few people who started PhD straight out of college and got screwed by still being dependents. I honestly don't understand why getting a stipend for doing research would be considered unearned.
It just isn't logical for most people to know that their unemployment income is also unearned income, and that you could be underpaying your taxes even after filling out the 1040 completely (and following the instructions in the 1040 instruction book).
Maybe this case is called out specifically, it doesn't apply to me so I haven't looked for it in the instructions, however it was just something that I ran across that made me scratch my head.