Command line formatter works only when IDEA isn't already running

If I run the formatter from the command line as explained at https://www.jetbrains.com/help/idea/command-line-formatter.html it only works when IDEA isn't already running.

This happens with IDEA 2017.2.1 on Windows 8.1 64-bit.

I would like to know if this is a bug or if it's the intended behavior.