A comment about simulation settings that may be affecting your results:

The "step_time" in "sample(0, step_time)" should not be smaller than the fixed-step solver's step size. 

As you describe, theoretically some window functions are defined over different indices (namely, 0..N-1 and 1..N). In my investigation of this problem it seems that no matter the window function chosen or the indexing of the input array, Maple is indexing the output of the window function as 1..N and this index conversion is being done "behind the scenes". In particular, for the Hann window, we define the indices as being 0 .. N-1, and for the Welch window we define them as being 1 .. N. It appears as though you want to get the N+1 values at indices 0 .. N for the Welch window; unfortunately, there's no way to obtain those directly from the SignalProcessing package. 

If you see any freezing issues during the installation process on Windows 10 machines, you will simply need to download a new Maple 2016.1 installer file and add the "--installfonts 0" parameter onto the installation launch command. This will bypass the font installation process, allowing you to install Maple with your deployment software. 

For a new link to the Maple 2016.1 installer file and the font installer contact support@maplesoft.com