ttsc --watch updates compiled files which are typically not touched by vanilla tsc

[dko-slapdash]

UPD: I thought it's related to --assumeChangesOnlyAffectDirectDependencies flag - https://devblogs.microsoft.com/typescript/announcing-typescript-3-8/ - but it's not. Even without this flag, ttsc overwrites the files in dist/, although their compiled output and themselves are both not changed (and tsc doesn't touch such files in similar sutuations).

# package.json
{
  "dependencies": {
    "nodemon": "^2.0.3",
    "ttypescript": "^1.5.10",
    "typescript": "^3.8.3"
  }
}

# tsconfig.json
{
  "include": ["src"],
  "compilerOptions": {
    // "assumeChangesOnlyAffectDirectDependencies": true,
    "baseUrl": "src",
    "outDir": "dist"
  }
}

# src/a.ts
export function aaa(): string {
  return "aaa";
}

# src/b.ts
import { aaa } from "./a";
export function bbb(): string {
  return aaa() + "/bbb";
}

# src/c.ts
import { bbb } from "./b";
export function ccc(): string {
  return bbb() + "/ccc";
}

In console 1:

yarn install
yarn ttsc --watch

In console 2:

yarn nodemon -w dist --verbose --exec "sleep inf" | grep "files triggering change"

In console 3:

echo "// test" >> src/a.ts
# Just touching is not enough, we need the file content to change.

Expected result (and actually this is what vanilla yarn tsc --watch shows):

[nodemon] files triggering change check: dist/a.js

Actual result with ttsc:

[nodemon] files triggering change check: dist/a.js
[nodemon] files triggering change check: dist/b.js
[nodemon] files triggering change check: dist/c.js

P.S.
If it stops reproducing, run rm -rf dist/* before ttsc.

P.P.S
I can be that vanilla tsc also recompiles b.ts and c.ts on changes in a.ts, but just doesn't write them since the compiled output is not changed (and ttsc doesn't have this "content comparison"). But then, what about --assumeChangesOnlyAffectDirectDependencies flag? Is it supported by ttsc the same way as it's supported by tsc?

[dko-slapdash]

Here is a GitHub repo with repro: https://github.com/dko-slapdash/ttsc-watch-issue

# all 3 files in dist/ are updated
yarn test-ttsc
echo "// test" >> src/a.ts

# vanilla tsc; only 1 file in dist/ is updated
yarn test-tsc
echo "// test" >> src/a.ts