--watch doesn't realize when --strict mode flags are changed

[DanielRosenwasser]

// ./foo.ts
declare function foo(): null | { hello: any };

foo().hello

// ./tsconfig.json
{
    "compilerOptions": {
    }
}

Run with --watch, and try toggling on/off --strict or --strictNullChecks.

Expected: Efforts appear and reappear when toggling.
Actual: Errors stay the same as initial run.