Strange Append behavior

[LiviuShiva]

It seems like for version 1.4.0 the Append function returns an empty Enumerable
Ex. I:
test = Enumerable()
test.append(1)
print(test)

Returns:
[]

Expected:
[1]

Ex. II:
test = Enumerable([1, 2, 3]).append(4)
test.append(5)
print(test)

Returns:
[1, 2, 3, 4]

Expected:
[1, 2, 3, 4, 5]

I suspect that the problem comes from the concat function

I noticed that there was a problem with the previous version as well:
Ex:
test = Enumerable([1, 2, 3]).append(6)
test.append(5)

Returns:
[1, 2, 3, 6, 5, 6]

Expected:
[1, 2, 3, 6, 5]