Ok, I guess I'm not sure what to do about it. I scanned the entire dropbox folder, and no threats were found. Then I thought the program itself was the problem, so I uninstalled it, deleted all my synced info, and re-downloaded and re-installed the program. Same result, except this time the temp file has a different name. Also checked that one on virustotal.com, and interestingly enough, it stated it was the same file as the one I had tried earlier today.
So what to do? The problem isn't with the files I have on dropbox, and it's not with the program itself. I don't disagree that there's an infection, but I don't know how to find and permanently remove it.