core language - Pick bug? level 0 matching

A previous discussion of this issue (Is there a bug in Pick?) accepted that matching at level 0 is not a bug in Pick. Was that correct? I am not yet persuaded.

Here is the documentation (http://reference.wolfram.com/language/ref/Pick.html): "Pick[list,sel,patt] picks out those elements of list for which the corresponding element of sel matches patt."

This clearly speaks of corresponding elements. It seems to me that either there is a documentation bug or there is an implementation bug. Why am I wrong? Furthermore, the documentation gives the obvious statement of intent, so I suspect an implementation bug.

Here is (yet) another example that illustrates how bizarrely unexpected is the current behavior:

x = Range[20]
Pick[x, x/2, _Integer]  (* works as expected *)

Pick[x, x/2, Except[_Integer]]  (* does not work as expected *)

I find it almost impossible to believe that Pick was intended to cause this simple use of Except to fail by matching the entire list x/2 rather than, as the documentation states, checking for a match in the corresponding element.

Note that I am not asking how to get the intended match; I realize that Except[_Integer|_List] will accomplish that in this case. Also, I am using Mma 9.

Comments

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