Serenity not recognize driver in serenity.conf when using 2 driver

[lilyhoang]

I start 2 driver to use 2 actors. Please refer sample project below:
https://github.com/lilyhoang/serenity-issue.
My issue is I config using firefox in serenity.conf file but when test failed, the next test will start 2 drivers Chrome instead of 1-Chrome, 1-Firefox.

@Managed(uniqueSession = true, clearCookies = ClearCookiesPolicy.BeforeEachTest, driver = "chrome")
private WebDriver firstBrowser;

@Managed(uniqueSession = true, clearCookies = ClearCookiesPolicy.BeforeEachTest)
private WebDriver aSecondBrowser;

I expect firstBrowser is CHROME, secondBrowser is Firefox.
Please help me