Oomek finalmente, tras varios intentos de pedir la solución por mi parte, me ha dado la solución en su foro en "Bug Reports":
"El comportamiento anterior del módulo de Animate probablemente fue causado por una laguna / error en el modo de atracción. Si necesita animar las 4 propiedades alfa del objeto ListBox, le sugiero que lo haga de la siguiente manera: "
fe.load_module("animate")
local flx = fe.layout.width
local fly = fe.layout.height
local flw = fe.layout.width
local flh = fe.layout.height
my_time <- 600
my_delay <- 1000
// Listbox
::OBJECTS <- {lbx = fe.add_listbox(flx*0.76, fly*0.33, flw*0.20, flh*0.64)}
OBJECTS.lbx.rows = 21
OBJECTS.lbx.charsize = 24
OBJECTS.lbx.align = Align.Left
OBJECTS.lbx.alpha = 255
OBJECTS.lbx.set_rgb(255,255,255)
OBJECTS.lbx.bg_alpha = 255
OBJECTS.lbx.set_bg_rgb(50,50,50)
OBJECTS.lbx.set_sel_rgb(255,0,0)
OBJECTS.lbx.sel_alpha = 255
OBJECTS.lbx.set_selbg_rgb(100,100,100)
OBJECTS.lbx.selbg_alpha = 255
local fadein_alpha_lbx = {when = Transition.ToNewSelection, property = "alpha", start = 255, end = 255, time = 1}
local fadein_bg_alpha_lbx = {when = Transition.ToNewSelection, property = "bg_alpha", start = 255, end = 255, time = 1}
local fadein_sel_alpha_lbx = {when = Transition.ToNewSelection, property = "sel_alpha", start = 255, end = 255, time = 1}
local fadein_selbg_alpha_lbx = {when = Transition.ToNewSelection, property = "selbg_alpha", start = 255, end = 255, time = 1}
local fadeout_alpha_lbx = {when = Transition.ToNewSelection, property = "alpha", start = 255, end = 0, time = my_time, delay = my_delay}
local fadeout_bg_alpha_lbx = {when = Transition.ToNewSelection, property = "bg_alpha", start = 255, end = 0, time = my_time, delay = my_delay}
local fadeout_sel_alpha_lbx = {when = Transition.ToNewSelection, property = "sel_alpha", start = 255, end = 0, time = my_time, delay = my_delay}
local fadeout_selbg_alpha_lbx = {when = Transition.ToNewSelection, property = "selbg_alpha", start = 255, end = 0, time = my_time, delay = my_delay}
animation.add(PropertyAnimation(OBJECTS.lbx, fadein_alpha_lbx));
animation.add(PropertyAnimation(OBJECTS.lbx, fadein_bg_alpha_lbx));
animation.add(PropertyAnimation(OBJECTS.lbx, fadein_sel_alpha_lbx));
animation.add(PropertyAnimation(OBJECTS.lbx, fadein_selbg_alpha_lbx));
animation.add(PropertyAnimation(OBJECTS.lbx, fadeout_alpha_lbx));
animation.add(PropertyAnimation(OBJECTS.lbx, fadeout_bg_alpha_lbx));
animation.add(PropertyAnimation(OBJECTS.lbx, fadeout_sel_alpha_lbx));
animation.add(PropertyAnimation(OBJECTS.lbx, fadeout_selbg_alpha_lbx));