Excluding with vim's wildignore

I found it more difficult than usual to get the wildignore setting working properly in vim, so I thought I'd document it here.

The wildignore setting is used in conjunction with the path and other settings such as wildmenu, and supposedly can be used to specify filename patterns that should be ignored when searching for files, for example using the find command.

I'm running a fairly modern version of vim (7.4) compiled with the +wildignore option:

dj@pipetree ~ $ vim --version | grep wildignore  
+cscope          +lispindent      +python3         +wildignore
dj@pipetree ~ $  

but specifying a pattern such as this:

set wildignore=node_modules/**  

or variations thereof, such as

set wildignore=**/node_modules/**  

or even

set wildignore=**node_modules**  

didn't have the desired effect. I'm wanting to exclude content from that folder (and the subfolders contained there) as they don't form part of the codebase I'm working on in my JavaScript projects.

What works for me is

set wildignore=/home/dj/**/node_modules/**  

In other words, an absolute path (I've tried using the tilde too, to no avail).

This is good enough for me, but it does irk me that something that should be so simple ... isn't.