This line creates a UTF8Reader whose autoclose is determined by _context.isResourceManaged() alone. In other instances autoclose is determined by _ioContext.isResourceManaged() || isEnabled(StreamReadFeature.AUTO_CLOSE_SOURCE) or equivalent (see YAMLParser).
This means that in cases where AUTO_CLOSE_SOURCE is enabled but isResourceManaged() is false, files are left open where the user expects them to be auto-closed in line with other class behaviors.