Using watch displays test results twice

[ezk84]

If I use the preferred development mode as per the README with the current version of karma, the reported results are output twice.

Here is an example project which reproduces the error.
gruntkarmadoubleoutput.zip
Run

npm install
grunt karma:continuous # to see expected output
grunt dev # and change a file in src to see erroneous double output

I've added two dummy assertions to demonstrate that it is double output and not just the same tests being run twice. The random numbers produced by Math.random are the same in both versions.

This seems to be because both the karma server and the client are writing the results to stdout.
If I create a similar karma.conf.js and run karma start and karma run on different consoles, each will output a version of the results.

Seems like grunt-karma should somehow set the karma runner to not output the results since the server (running in the background) will already output them. Alas, there doesn't seem to be a configurable way to do this from grunt-karma.