The top voice has fingerings, the bottom voice has fingerings. Rosegarden does a middling decent job of displaying all of this on one staff, but the LilyPond export is utterly illegible crap.
Rosegarden prints the 4 on the first melody note of "Romanza" above the note, and that works fine. As exported, this 4 gets printed way below the staff, below the middle voice notes, and totally colliding with the ledger lines for the bass note and the 3 for the triplet. It's a huge mess.
Best we can do is probably some hack to use manual LilyPond overrides to try to mimic Rosegarden's placement.
It looks fiddly, but possible: