Yangtools fails to parse module with description following a YANG extension

Yangtools fails to parse a module if that module has a YANG extension (e.g. "vendor:foo") followed immediately by a description statement.

The error in the log is "extraneous input 'output' expecting

', 'uses', 'typedef', 'status', 'reference', 'list', 'leaf-list', 'leaf', 'grouping', 'description', 'container', 'choice', 'anyxml', IDENTIFIER} in module"...