LCD cutting out when HDMI connected

[Grifter]

Is there a way around this ?
I bought the teradek vidiu streaming device to stream from the camera only to discover the lcd screen at the back of the dslr cuts out when connected.
I should add its the 5dmk3

Edit: ok i know now what the story is

[leonetti]

Then what is the storie?

I saw black stripes on both sides and top and downside appr. 10 percentage of the 1920x1080 picture if I set ML to hide all information.  (In movie mode in live view).

And! If I switch to M photo shooting mode, and I turn all info off then there are dustygreen stripes upper side and downside :/