After enabling staticsaver.include_category in the system settings, folders are not automatically created on disk. If I prefix the generated filename with "foldername/", the folder is created.
Replicated on v2.2.15 and 2.3.1
It seems that the following lines in staticsaver.js are the issue as if the condition is true only the chunk name is used:
if (staticFile.getValue() == '') {
setValue(staticFile, nameInput.getAttribute('value'));
} else {
getRequest();
}