Inverse of Plan Legendre Transform alters input?

Not sure if this is an expected behavior or not, what is the resulting vector?

```
P = Legendre()
x = chebyshevpoints(Float64, 10, Val(1))
p = plan_transform(P, x, 1)
v = rand(10)
v_copy = copy(v)
p\v 
v ≈ v_copy  #false

```