When you say upload, do you mean when you import the file from your computer to your empeg?

Yes

If I'm reading this correctly, you're saying the MP3 file has "(17)Rock" set as its genre ... Where are you seeing this value displayed in jEmplode -- if the playlist table view or somewhere else?

The 3 following screendumps probably explain my comments a little more:
(1) the first part (hexdump) of the original mp3 file.
(2) the genre as displayed in my ID3 tag editor ("Easytag")
(3) the result in jEmplode (the existing mp3, and the freshly added mp3 (with dupe check disabled)).

As can be seen, the new upload with jEmplode 47 results in the "(17)Rock" genre (in contrast to the existing one, uploaded with the pre-47 version).

NB: According to the ID3V2.3 specs, it is possible to have the old ID3V1.x numerical code to be present in the ID3V2.3 genre code (from this site)

NB2: It is still possible that this is due to incorrect upgrade from 44 to 47, so I'm really interested if anyone can confirm or deny this behaviour in their own setup with v47