intern test runner failing to execute async tests

I am using intern's client.html for running unit tests and test runner for functional tests. But after adding few async tests in my unit tests, test runner is failing as the test runner executes both unit and functional suites.

I have all the tests as shown below:

suites: [
'tests/unit/all'
],
functionalSuites: [
'tests/functional/all'
]

When the async tests are executed by test runner, it is not waiting for the async tests to complete. But the same async tests work fine for the client.html