confusing behaviour in riffle()

[RobinHankin]

This is confusing:

> riffle(1,2)

[1,] 1 2 2
[2,] 2 1 3
[3,] 3 3 1
> riffle(c(1,2))

[1,] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2
[2,] 2 2 2 2 2 2 2 2 2 2 2 2 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5 5 5 1 1 1 1 1 1 1
[3,] 3 3 3 4 4 4 5 5 5 5 5 5 2 2 2 5 5 5 2 2 2 2 2 2 4 4 4 6 6 6 3 3 3 4 4 4 5
[4,] 4 5 5 3 5 5 3 3 4 4 6 6 3 5 5 2 2 6 3 3 4 4 6 6 2 2 6 2 2 4 4 5 5 3 5 5 3
[5,] 5 4 6 5 3 6 4 6 3 6 3 4 5 3 6 3 6 2 4 6 3 6 3 4 3 6 2 3 4 2 5 4 6 5 3 6 4
[6,] 6 6 4 6 6 3 6 4 6 3 4 3 6 6 3 6 3 3 6 4 6 3 4 3 6 3 3 4 3 3 6 6 4 6 6 3 6

[snip]
[1,] 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5
[2,] 2 2 2 2 2 2 2 2 4 4 4 4 4 4 4 4 4 4 4 4 6 6 6 6 6 6 6 6 6 6 6 6
[3,] 4 4 6 6 6 6 6 6 1 1 1 2 2 2 2 2 2 6 6 6 1 1 1 2 2 2 2 2 2 4 4 4
[4,] 6 6 1 1 3 3 4 4 2 2 6 1 1 3 3 6 6 1 2 2 2 2 4 1 1 3 3 4 4 1 2 2
[5,] 1 3 3 4 1 4 1 3 3 6 2 3 6 1 6 1 3 2 1 3 3 4 2 3 4 1 4 1 3 2 1 3
[6,] 3 1 4 3 4 1 3 1 6 3 3 6 3 6 1 3 1 3 3 1 4 3 3 4 3 4 1 3 1 3 3 1
> 

[the second line calls riffle(c(c(1,2),c(1,2)))]. Should be either documented or trapped.