When creating Content in certain way the PlatformUI cache is not updated, resulting in Content not being displayed in PlatformUI.

This is easily reproducible using our Docker setup (currently running on Travis, see https://travis-ci.org/ezsystems/PlatformUIBundle/jobs/372056679 for an example).
The failing tests are marked with @EZP-29193-exclude-varnish tag.
Steps are as follows:
Running behat tests:
1. Login as admin to PlatformUI
2. Create Content using our API (for example: a folder in eZ Platform)
3. Go to Content -> Content Structure, open UDW:
The "eZ Platform" folder has an arrow next to it like there are additional items, but none are displayed.
Example: http://recordit.co/bJHAEQat5V

Sadly, this does not mean it's easily reproducible in other ways.

What I've tried: (manually)
1. Login as Admin
2. Create Content using Command (attached)
3. Go to Content -> Content Structure
4. Open UWD

Result: content is displayed

I've tried to narrow it even more:

• invoking the code of the command from the Behat tests results in the same failure
• invoking the command from Behat tests

  shell_exec("php app/console content:create -e behat");

  works (issue does not occur), UDW correctly loads content

Issue does not occur without Varnish.
I've also attached varnish logs for both of the cases mentioned above (invoking command from test code and running shell_exec).

When the issue occurs it occurs 100% of the time (I've tried adding waiting after the Content is created - it did not make a difference).

Because I was not able to reproduce it manually (without running Behat) I've set the priority to Medium, as I'm not able to tell where the problem is.