Debugging IntelliJ which is debugging Javascript

I have a language which transpiles to Javascript. To debug it, I do as follows:

1. Fire IntelliJ A (the latest Ultimate EAP, (IU-162.2228.15  EAP  2016.2.5)

2. Select plugin debug configuration and click Debug

3. That fires IntelliJ B (Same EAP)

4. In B, I select JS debug configuration and click Debug.

By the time I do 4, the built-in HTTP server port (63342 if I am not mistaken?) is already taken by A.

So, I explicitly changed the port: in A,

And in B, 

I am getting this:

I tried to change the port in chrome-extension://for JetBrains IDE Support to various different values, including 63343, 33333, etc. Does not seem to help. What am I doing wrong?