Why does argparse give me a list-in-a-list?

I just noticed a behavior in argparse that puzzled me (guess I'd never used it for a dumb list of files before):

import argparse
parser = argparse.ArgumentParser()
parser.add_argument('multi', action='append', nargs='+')
print(parser.parse_args())

This gives me the output:

~$ ./testargs.py foo bar baz
Namespace(multi=[['foo', 'bar', 'baz']])
~$ 

I expected multi to be ['foo', 'bar', 'baz'], not a list within a list. As-is, I'll have to grab args.multi[0] before processing, which isn't a big deal, but feels like an ugly wart, and I'd like to understand why it's there.

Am I doing something silly in add_argument, or is this just an unavoidable quirk?