discardOldKeys removes phrases when shared by multiple files

[chrys1110]

Describe the bug

with discardOldKeys: true already translated keys get removed when multiple files share the same namespaces.
i.E Both depend on namespace 'errors' and import them with useTranslation.
fileA uses errorA. fileB uses errorB.
Babel extracts errorA when compiling fileA and dismisses errorB, and vice versa. Already translated terms get removed unfortunately.

How to reproduce

Described above.

Babel configuration:

{
    "presets": [
        "next/babel"
    ],
    "plugins": [
        [
            "i18next-extract",
            {
                "locales": [
                    "en-US",
                    "de"
                ],
                "defaultNS": "common",
                "discardOldKeys": true,
                "jsonSpace": 4,
                "useI18nextDefaultValue": [
                    "en-US"
                ],
                "outputPath": "public/static/locales/{{locale}}/{{ns}}.json",
                "customUseTranslationHooks": [
                    ["next-i18next", "useTranslation"]
                ]
            }
        ]
    ]
}