Oh, I see, thanks for your feedback. From looking at the source code, it seems that the panel is looking for a lowercase blueprint file, so that means that all text files should be lowercase indeed.
This is the find() function from blueprint.php:
static public function find($id) {
if(is_a($id, 'Page')) {
$name = $id->intendedTemplate();
$file = static::$root . DS . strtolower($name) . '.php';
if(!file_exists($file)) {
$name = $id->template();
$file = static::$root . DS . strtolower($name) . '.php';
if(!file_exists($file)) {
$name = 'default';
}
}
...