Matched problems dropped when running in container

Describe the bug
A problem matcher enabled using a 'normal' run step in a job running in a container drops all issues with "Dropping file value ... Path is not under the workflow repo." Removing the container option from the workflow file (such that it runs on ubuntu-latest) and leaving all configuration unchanged does not drop the issues and creates annotations as expected.

To Reproduce
Steps to reproduce the behavior:

1. Create a workflow with a configuration similar to (the example uses eslint):

name: PR Linting

on:
  pull_request:
    branches: [ develop ]

jobs:
  lint:
    name: Lint
    runs-on: ubuntu-latest
    container:
      image: node:14.13.1

    steps:
      - uses: actions/checkout@v2

      - name: Enable problem matcher
        run: echo "::add-matcher::.github/problem-matchers/eslint.json"

      - name: Run linter
        run: npm run lint

2. Add the actual problem matcher (I used the multiline example: https://github.com/actions/toolkit/blob/main/docs/problem-matchers.md)
3. Run it
4. Warnings / errors will be highlighted, but no annotations created.
5. Remove the container section from the definition
6. Warnings / errors will be highlighted and annotations will be created.

Expected behavior
Matched issues resulting in annotations when running in a container.

Runner Version and Platform

2.273.5 on GitHub.com

OS of the machine running the runner? OSX/Windows/Linux/...
Ubuntu 18.04.5

What's not working?

Job Log Output

See screenshot

The issue names no source files or tests. Start by reproducing the workflow with the container and problem matcher, then inspect the runner logs around the dropped file paths; done means matched problems from container jobs produce annotations without the path warning.