bk 9920 problem... help needed before returning product...

okay guys, i've discovered sthg... in fact i can program and run perfectly with the BEC enable, that mean that I can't use my rx pack... I never tried to do this because specs said that i had to use a rx pack with 2x7cells...
It was a little satisfaction... but now i would like to run my sterring servo in 6V!!!
After that I tried to plug the black jumper on the controler, and in this config I can run my servo at 6V!!!
But please can you confirm that there no risk to run the rx pack, plus the black jumper plugged onto the controler??? if it's ok for you all i will try to run these settings...

ps: i tried to do the programming procedure with my stock tq3 rx and tx, it doesn't work at all...