Hi,
Well, yes. At this point it is pretty clear what is happening.
The "new" 2.x version of the IDE introduced a few changes.
The first one: It is now "code aware", and this new feature requires continuous processing of the sketch. What this means in reality is this: If you have an IDE window with a sketch opened, then for every major change in the code it will take a few seconds to recompile, rebuild and recheck your code. While it is doing this, the whole IDE window is blurred out, and on the bottom-left corner of the IDE you will get a message telling you that it is doing so.
Which is great for someone who is just hooking up a board to the PC and code it for fun.
It is NOT great however, when you have 2+ screens, with 2+ IDE windows opened, with 2 different codes.
Say for example: On the left screen I have my Teensy code that is the communication hub between my X-Plane Flight sim and the rest of my Atmega328 driven peripherials. And on the right screen I have my Uno code that should be running a Keyboard driver and use some kind of a communication protocol to communicate with the other board as required. Constant recompiling of the code takes up valuable time and resources, and the new version has no way to kill this crap. So this is reason 1 for downgrading, and NEVER upgrading in my lifetime again.
The second one: I noticed, that if I loose focus on an IDE window, then that window becomes blurred. Which is an issue, if you try to monitor 2 projects communicating with each other and the PC in real time. Especially, if you are like me, and like to have 2 IDE windows plus a browser with the Language reference and the GNU C++ reference opened at the same time for efficiency. The old 1.x versions never did this, and honestly if I could just find a plugin for my IntelliJ IDEA then I would ditch this IDE altogether. The only reason why I am using this IDE is due to the fact, that the Arduino language specific pin control is easier for me than a pure C++ based one.
That being told, I can not be bothered with experimenting. My preferred IDE has support for C++, and I am pretty sure I can just write a language file for the Arduino specific commands and then use my IntelliJ IDEA for writing the code and syntax checks. At this point I could program an Arduino board in Notepad++, and the only reason I need the Arduino IDE is to compile and upload the project.
Or I can just bite the bullet, and ditch everything BUT the Teensy, and go with the TI MSP430 MCU family, as their IDE is at least usable, and still uses Arduino language...