Inconsistency between 1D NFFT and (N,1)-dimensional NFFT

The result of a 1D NFFT of length N and a (N,1)-dimensional NFFT are quite inconsistent.
Here is a MWE:

```
using NFFT
M = 4
x1 = collect((-Int(M/2)):(Int(M/2)-1))/M
N1 = M
p1 = NFFTPlan(x1, N1) # 1D plan
f1 = ones(N1)
o1 = nfft(p1, complex(f1))

N2 = (M,1)
x2 = [x1 zeros(M)]
p2 = NFFTPlan(x2', N2)
f2 = ones(N2)
o2 = nfft(p2, complex(f2))

display(o1), display(o2)
```

Perhaps there is some minimum size requirement for each dimension of a multi-dimensional NFFT? If so then should NFFTPlan throw an error if that requirement is not met?

1D NFFT is working great for me but 2D NFFT is not behaving as I am expecting, so this (N,1) case is an example of a test I am doing to try to diagnose my 2D issues...