Yarn add --modules-folder not downloading all deps

[enfoqueNativo]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
Sequential adds made through composer script don't complete installation of all packages, however yarn.lock says they're installed.

Any composer.json with the following lines should be enough. Run it through composer run-script post-install-cmd

"post-install-cmd": [
            "yarn add font-awesome@4.7  --modules-folder tmp_assets/",
            "yarn add bootstrap@3.3  --no-dev --modules-folder tmp_assets/",
            "yarn add respond.js@1.4  --modules-folder tmp_assets/",
            "yarn add html5shiv@3.7 --modules-folder tmp_assets/"
]

What is the expected behavior?
Download and install the four packages on the specified folder.

Please mention your node.js, yarn and operating system version.
Node: v8.11.4
Yarn: 1.12.3
OS: OpenSuse Leap 15

[rally25rs]

To reproduce the issue, can just run the 4 yarn commands from the command line without the post-install-cmd stuff...

For some reason yarn seems to think that the previous packages are extraneous and deletes them.

[rally25rs]

This might be related to #5419

[enfoqueNativo]

To reproduce the issue, can just run the 4 yarn commands from the command line without the post-install-cmd stuff...

For some reason yarn seems to think that the previous packages are extraneous and deletes them.

The behaviour on cmd line it's really weird too, i've executed the lines one by one followed by an "ls" of the destination folder. Dependencies comes and go with every cmd.

debug.txt

There's no node_modules folder on the directory, it seems it never gets created.