xfce4-terminal seems to handle (Ctrl+)Shift+Up/Down on its own, it scrolls by a line. I guess it should be removed. Shift+Up/Down is probably too intrusive, apps might want to use it for their own purpose (e.g. for selecting text in mcedit). For Ctrl+Shift+Up/Down, it's VTE's built-in behavior is to scroll by a line, pretty much the way xfce4-terminal does it anyway, so there's not much point replicating it. (Note: There's a small difference with VTE-0.44's smooth (i.e. per-pixel) scrolling feature. VTE's built-in Ctrl+Shift+Up/Down scrolling intentionally snaps the viewport to whole cells, whereas xfce4-terminal's implementation leaves it at partial lines being shown.) (See also bug 1927.)
Oops, just realized there's a corresponding checkbox in the Prefs window. Anyway, I don't see too much point in this feature, as well as it's an FYI that with smooth scroll, Ctrl+Shift+Up/Down now works slightly differently than if you disable this option.
Thanks, removed by https://git.xfce.org/apps/xfce4-terminal/commit/?id=4cf4d385b952e770d2e353941dc14934d9bb8d8c
Version 0.8.1 has introduced new hidden option MiscUseShiftArrowsToScroll which restores old scrolling behavior; the default value is FALSE i.e. Shift+arrows does not scroll.