AdditionalLibraryRootsProvider.getRootsToWatch does not include subdirectories

Hi,
I have implemented custom AdditionalLibraryRootsProvider to add root directory X to External Libraries. I also overridden getRootsToWatch method to watch directory X for changes. On startup everything works as should be, in External Libraries tab I see root X with all its content, however If I add new directory inside X, in the file tree, the new directory is seen without its content.

Ex.: 
Creating Folder Y with files a, b inside X root.
expected view in file tree:

  External Libraries:
    X:
       Y:
           a
           b
Actual view (files a, b are missing):
  External Libraries:
    X:
        Y:

After restarting IDE Everything is presented as expected. What I am doing incorrectly? How can force to watch new folders recursively?

My AdditionalLibraryRootsProvider implementation:

class NpmSourcesLibraryRootProvider : AdditionalLibraryRootsProvider() {

    override fun getAdditionalProjectLibraries(project: Project): MutableCollection<SyntheticLibrary> {
        val rootDirectoryFile = SourceCacheDirectory.getSourceCacheDirectoryFile()
        val library = NpmSourcesSyntheticLibrary(rootDirectoryFile)
        return mutableListOf(library)
    }

    override fun getRootsToWatch(project: Project): MutableCollection<VirtualFile> {
        val rootDirectoryFile = SourceCacheDirectory.getSourceCacheDirectoryFile()
        return mutableListOf(rootDirectoryFile)
    }
}

class NpmSourcesSyntheticLibrary(private val libraryRootDirectory: VirtualFile) : SyntheticLibrary(), ItemPresentation {

    override fun getPresentableText(): String = "npm sources"

    override fun getIcon(unused: Boolean): Icon? = null

    override fun getSourceRoots(): Collection<VirtualFile> = libraryRootDirectory.children.toList()

    override fun equals(other: Any?): Boolean {
        if (this === other) return true
        if (javaClass != other?.javaClass) return false
        other as NpmSourcesSyntheticLibrary

        if (libraryRootDirectory != other.libraryRootDirectory) return false

        return true
    }

    override fun hashCode(): Int = libraryRootDirectory.hashCode()
}