Cli option mutual exclusion not working in all cases

[drennalls]

I have an app with a simple requirement. Allow the user to save some data to a file, with an autogenerated name or a user-specified name. If --out is used then a generated filename (based on some data properties) is used. For a custom filename the user can use --out-file instead. I would have liked to just have one --out option that can either take an argument or be used on it's own, but there doesn't seem to be a way to do that. So sticking to mutually-exclusive --out and --out-file options. However, the mutual-exclusion check doesn't work depending on the order.

..Here's a dummy app to demonstrate the problem.

#!/usr/bin/env python
from plumbum import cli
from pprint import pprint

class MyApp(cli.Application):
    _out_format = cli.SwitchAttr("out-format", cli.Set('json', 'yaml'), default='json',
                                 help="Data format")
    _out_flag = cli.Flag("out", help="Save data using an auto-generated filename",
                         excludes=["out-file"])
    _out_file = cli.SwitchAttr("out-file", str, help="Save data using a specific filename", default=None, excludes=["out"])

    def main(self):
        print("out={}\n,out-file={}\n,out-format={}\n".format(self._out_flag, self._out_file,
                                                             self._out_format))

if __name__ == "__main__":
    MyApp.run()

Usage..

Usage:
    test.py [SWITCHES]

Meta-switches
    -h, --help                               Prints this help message and quits
    --help-all                               Print help messages of all subcommands and quit
    -v, --version                            Prints the program's version and quits

Switches
    --out                                    Save data using an auto-generated filename; excludes --out-file
    --out-file VALUE:str                     Save data using a specific filename; excludes --out
    --out-format VALUE:{'yaml', 'json'}      Data format; the default is 'json'

..Mutual exclusive works in this case..

~/misc/test.py --out --out-file --out-format json
Error: Given --out, the following are invalid ['--out-file']
------
Usage:
    test.py [SWITCHES]

Meta-switches
    -h, --help                               Prints this help message and quits
    --help-all                               Print help messages of all subcommands and quit
    -v, --version                            Prints the program's version and quits

Switches
    --out                                    Save data using an auto-generated filename; excludes --out-file
    --out-file VALUE:str                     Save data using a specific filename; excludes --out
    --out-format VALUE:{'yaml', 'json'}      Data format; the default is 'json'

But not in this case

~/misc/test.py --out-file --out --out-format json
out=False
out-file=--out
out-format=json

The "--out" is eaten up as the argument for --out-file instead of reporting an error.