Occasional warnings during auto-export

Steps to reproduce (may need several attempts )

1) Get a fresh project from the archetype, build and run it.
2) Go to Essentials, install the Events feature
3) Watch the log messages

When you get log messages, they are complaints that a certain config definition is attempted to be merged into the ConfigurationModel twice. I.e. it says that a certain property already exists with identical name, and both the new definition and the configuration already existing in the model point to the exact same *.yaml source in the exact same module - the one that has just been auto-exported (upon Essentials importing the corresponding nodes and properties into the repository).

Ate and I weren't able to reliably reproduce and debug this phenomenon. It may take a few attempts to reproduce this, which suggests that the problem is cause by some race condition.