I was going to check Estel's ISO problem when I found out my device didn't support 720p anymore (and I am pretty positive it did)...
I reinstalled everything 720p related + freemangordon's latest camera-ui2. His version is 1.1.29.2+0cssu7 and I had 1.1.29.2+0cssu8 (CSSU update replaced his version?). Reboot and it works again!

Back to Estel's problem: in both versions (0cssu7 and 0cssu8) manual ISO on both video and pictures does not black out the viewfinder and captured output is fine also.