Merged files ember-cli addon

I created an ember-cli addon and added some .properties files to the app folder. In my app which uses the addon I also have some .properties files and want all of them to be converted to JSON files. I managed to get the conversion right, but for some reason it is only picking the .properties files from the app, the .properties files from my addon are not included. It looks like they aren't merged into the app folder (the files are all named differently).

So my question is, does every file get merged? Or only .js and .css files?

Note: I'm applying the conversion in the brocFile by creating a tree and merging it with the app tree (at this point I'm missing the .properties files from the addon).