composer -a shows version 999999-dev

[codekandis]

When I execute composer -a codekandis/phlags --format json

No composer.json found in the current directory, showing available packages from packagist.org
...
"versions": [
    "9999999-dev",
    "3.0.0",
    "2.0.0",
    "1.2.0",
    "1.1.0",
    "1.0.0",
    "dev-development",
    "dev-master"
]

The output of the versions shows a 999999-dev which is confusing me. Is it a faulty packagist version, which isn't shown in the frontend, or is it a version by purpose for composer?

This issue isn't related to the mentioned specific package. It is related to every package.
This issue isn't related to the JSON formatted output. The mentioned version shows up in the default output, too.