Concentration extrapolation with AUCall goes up when it should go down

[billdenney]

extrapolate.conc(
   conc = c(1, 0), time = 0:1,
   time.out = 0.75,
   clast = 1,
   auc.type = "AUCall"
)
# [1] 0.75

The value should be 0.25