Hi I did not get this bug after reset to factory settings. It came after installing SPMC, Firefox Beta, MX Player, ES File Explorer and Weather Online Pro. The growing black bar grows after several times pressing OK button. Firmware version is 1.2.6, Zidoo X9s. Here is the video:
So, if this help, the same is with firmware version 1.2.3. There is another bug in settings -> Language & Input -> Android Keyboard Settings (AOSP) -> Apperance & Layouts -> Theme. I can only choose Material Light. The another choices, Material Dark or Holo White or Holo Blue, i can't choose. This bug was in firmware version 1.2.6 too. Here is the video:
I have done several factory reset. The problem with the keyboard layout continues, you can't select except material light. The problem with the Settings -> Apps was: After pairing via bluetooth with the Amazon Fire TV Remote not voice operated: https://www.amazon.com/Replacement-Remote-Amazon-Fire-Stick/dp/B00LORGAG6 and its use comes to the bug. After separating the Bluetooth connection with the Amazon Fire TV Remote everything is normal in apps. Other, what I noticed, was that the keyboard after factory reset was off, I also believe in firmware 1.2.6 too.
