Simple animations not working anymore

It probably happened after the update from 5.2 to 5.3 or something. The animations, that were working dont work properly anymore. I even abandoned my cool project because of this bug. Now I made a new project, and the same bug happened. This is driving me crazy, I will now post an exact description of this bug, and I hope that someone can help me with this.

This is the walk animation in the editor:

https://www.dropbox.com/s/g2gkd6b29vh31xj/AutoScreenRecorder_01%20May.%2016%2010.58.avi?dl=0

It works with this animator ingame:

Animator:

Ingame Animation:
https://www.dropbox.com/s/xbafpp67llgxvjd/AutoScreenRecorder_03%20May.%2016%2011.02.avi?dl=0

However, when I make a simple change in the animator, and add the idle animation to the animator:

Animator:

Animation in game:
https://www.dropbox.com/s/fajhaq5srspdkzp/AutoScreenRecorder_02%20May.%2016%2011.01.avi?dl=0
(The right arm is not moving)
(When I remove the right arm rotation from the idle animation, then the run animation works again, but why does the idle animation even have an effect, although it doesnt play?)

Project:
https://www.dropbox.com/sh/r7qqyd0abbwopq6/AABrvuv2DGkPjy2WQzCADusSa?dl=0

Why does this happen? What influence could the idle animation have on the run animation? Please help, I cant find anything similar on the internet.

Fixed the problem by setting all interpolations to eulerangles. But it is a unity bug isnt it?