Comment 1:

filepath.Walk's WalkFunc (http://golang.org/pkg/path/filepath/#WalkFunc) is documented
as:
"If there was a problem walking to the file or directory named by path, the incoming
error will describe the problem and the function can decide how to handle that error
(and Walk will not descend into that directory). "
That is, it returns the stat error for that name.
But Walk is implemented using (*os.File).Readdir
(http://golang.org/pkg/os/#File.Readdir), which was changed in
https://code.google.com/p/go/source/detail?r=100a10512ea4#
... to match its documentation.
That changed the behavior of filepath.Walk to now bail on any errors, rather than call
the WalkFunc callback with a (problemFilename, nil, errFromStat).
A fix was proposed at https://golang.org/cl/16100043/

Comment 2:

Status changed to Duplicate.

Merged into issue #6656.