Build mode ignores inherited --pretty flag when run through lerna

TypeScript Version: 39.4

Search Terms: build pretty

"Code"
I am currently in the process of converting a project to a monorepo. Here I noticed that tsc -b seems to ignore the --pretty flag defined in a parent tsconfig when its run through lerna (with the stream flag set to true).
The project is set up as follows
tsconfig.json: pretty => true
tsconfig.build.json: extends from tsconfig.json
package/package-name/tsconfig.build.json: extends from ../../tsconfig.build.json
package/package-name/package.json defines the npm scripts

"scripts": {
  "prebuild": "gulp prebuild",
  "build": "tsc -b tsconfig.build.json",
}

The pretty flag only works sometimes:
If I manually execute npm run build in the package dir, the tsc output is pretty.
If I execute lerna run build --scope=package-name, the tsc output is NOT pretty.
If I execute lerna exec --scope=package-name -- npm run build, the tsc output is pretty.
If I manually add the --pretty flag to the npm script ("tsc -b tsconfig.build.json --watch --pretty"), the tsc output is pretty in all the cases.

Although this might be caused by lerna, I suspect this is actually a bug in TypeScript, because the prebuild output from gulp is colored (pretty) in all the cases I mentioned and manually adding the flag also works.

Expected behavior:
CLI output is "pretty"

Actual behavior:
It is not

Playground Link: not applicable

Related Issues: https://github.com/microsoft/TypeScript/issues/30282

Start by reproducing the three command forms: npm run build in the package directory, lerna run build --scope=package-name, and lerna exec --scope=package-name -- npm run build. Inspect how tsc -b reads the chained tsconfig.json files and handles --pretty when invoked through lerna. Done means the inherited pretty setting produces consistent CLI output, or the issue is shown to belong to lerna instead.