Problem with grabbers' priorities

I have OSMC (latest version) installed on a RPi 3, which is connected with an arduino Uno (controlling the leds).
On the RPi 3 it's connected a UTV-007 video grabber.
Everything works as expected, but I am having a problem with the grabbers priorities.
I can not use the internal frame grabber and external "at the same time".
It will only work one at a time (based on the priorities).
I have tried to give higher priority to the external, just to give it a test, but as it is obvious, it only gave me image from the video card grabber (external). I also tried to enable "Kodi Checker" (I did not install anything on the OSMC, just ticked the option on hypercon - IP: 127.0.0.1 (localhost), but, it did not work as well.

So, to sum up:

• If I leave the conf at the default configuration (internal: 890, external: 900), only the internal works, even if the external video grabber receives image.
• If I change the conf to: internal 900, external 890, only the external works, even if OSMC is playing a movie.

Any ideas?

Thanks in advance!

Edit/TL;DR: to be even more specific, the OSMC can not detect which frame grabber I want to use. What I want, is the obvious: If I'm watching a movie or just use the RPi, to use the internal, if I am using another source of video (watching TV e.t.c.), to use the external.

Found the solution.

I also had to turn on "Proto/Json Forward".