[R] Reduce does not work with data.table?

[James Hirschorn]

Reduce is failing when applied to a list of elements of class 
data.table. Perhaps this is a bug?

Example:

library(data.table)

dt1 <- data.table(x = 1:3, y = 4:6)
dt2 <- data.table(x = 4:6, y = 1:3)
dt3 <- data.table(x = 0:-2, y = 0:-2)

# This works fine
dt1 + dt2 + dt2
#    x y
# 1: 5 5
# 2: 6 6
# 3: 7 7

# But:
dt_list <- list(dt1, dt2, dt3)
Reduce("+", dt_list)
# Error in f(init, x[[i]]) : non-numeric argument to binary operator
# In addition: Warning message:
# In Reduce("+", dt_list) :
#   Incompatible methods ("Ops.data.frame", "Ops.data.table") for "+"

If I use data.frame instead of data.table, Reduce works properly.