Some array settings like custom xsl files cannot be defined in default scope with semantic configuration. This forces bundle developers who relies these kind of settings to provide additional installation steps (e.g. for TagsBundle).
Workaround is to implement a compiler pass that does the job (e.g. EmbedTagBundle, but it still doesn't use semantic config validation and proper processing/mapping.
This is due to default scope not being considered as a siteaccess when merging values across scopes.