Stryker not closing correctly with low number of mutants

[nicojs]

The latest and greatest Stryker v0.10.2 doesn't seem to close correctly with a low number of mutants. See this example repo:

https://github.com/nicojs/stryker-typescript-issue394

It first creates way too many sandboxes and later only closes the one that actually ran tests (which is 1):

[2017-09-27 08:51:04.545] [INFO] SandboxCoordinator - Creating 7 test runners (based on CPU count)
[2017-09-27 08:51:04.549] [DEBUG] Sandbox - Creating a sandbox for files in C:\z\github\nicojs\stryker-typescript-issue394\.stryker-tmp\sandbox5322435
[2017-09-27 08:51:04.551] [DEBUG] Sandbox - Creating a sandbox for files in C:\z\github\nicojs\stryker-typescript-issue394\.stryker-tmp\sandbox6179253
[2017-09-27 08:51:04.552] [DEBUG] Sandbox - Creating a sandbox for files in C:\z\github\nicojs\stryker-typescript-issue394\.stryker-tmp\sandbox7459993
[2017-09-27 08:51:04.553] [DEBUG] Sandbox - Creating a sandbox for files in C:\z\github\nicojs\stryker-typescript-issue394\.stryker-tmp\sandbox1805168
[2017-09-27 08:51:04.554] [DEBUG] Sandbox - Creating a sandbox for files in C:\z\github\nicojs\stryker-typescript-issue394\.stryker-tmp\sandbox7940097
[2017-09-27 08:51:04.555] [DEBUG] Sandbox - Creating a sandbox for files in C:\z\github\nicojs\stryker-typescript-issue394\.stryker-tmp\sandbox2232950
[2017-09-27 08:51:04.556] [DEBUG] Sandbox - Creating a sandbox for files in C:\z\github\nicojs\stryker-typescript-issue394\.stryker-tmp\sandbox9039988
[2017-09-27 08:51:04.560] [DEBUG] Sandbox - Creating test runner 0 using settings {port: 9234}
[2017-09-27 08:51:04.566] [DEBUG] Sandbox - Creating test runner 1 using settings {port: 9235}
[2017-09-27 08:51:04.571] [DEBUG] Sandbox - Creating test runner 2 using settings {port: 9236}
[2017-09-27 08:51:04.575] [DEBUG] Sandbox - Creating test runner 3 using settings {port: 9237}
[2017-09-27 08:51:04.580] [DEBUG] Sandbox - Creating test runner 4 using settings {port: 9238}
[2017-09-27 08:51:04.585] [DEBUG] Sandbox - Creating test runner 5 using settings {port: 9239}
[2017-09-27 08:51:04.591] [DEBUG] Sandbox - Creating test runner 6 using settings {port: 9240}