Black and flashing screen after World of Warcraft upgrade

I have run into some problems after World of Warcraft upgrade. Screen is just black and constantly flashing. What is up with that? In addition, why are all those upgrades and patches released since release? I cannot believe that there are that many bug in the game. Did the developers made big mistakes, and they are now solving all o f them?

That black and flashing screen is very strange problem. I have never heard about anything similar. The upgrades and patching is needed to improve the game and to implement new quests, items and the rest stuff that is fun in the game. Can you imagine if the game is never upgraded or patched, and to finish all of the available quests. What would you do then? This kind of games needs to be regularly patched. World of Warcraft is very popular MMORPG, so it has many active players who are improving the game experience.