Impossible to exclude original declaration file from module #21189

TypeScript Version: 2.6.2
It is impossible to exclude or override d.ts files that are located in root of npm module.

For instance I have dependency on module named mymodule.
It contains declaration file in ./node_modules/mymodule/index.d.ts which is poorly made.
I have custom written declaration for it in ./@types/mymodule/index.d.ts
There're defined typeRoots in compilerOptions in ./tsconfig.json

{
    "compilerOptions: {
        "typeRoots": [
            "node_modules/@types",
            "@types"
        ]
    }
}

Than I added next rows (options above remained):

{
    "compilerOptions: {
        "typeRoots": [
            "!node_modules/mymodule",
            "!node_modules"
        ]
    },
    "exclude": {
        "node_modules/mymodule/index.d.ts"
    }
}

Expected behavior:
mymodule/index.d.ts getting ignored by compiler

Actual behavior:
mymodule/index.d.ts overrides my custom definitions