System Information
Operating system: Windows
Graphics card: GTX 1650 Max-Q`

Blender Version
Broken: v2.81a, v2.81, v2.82

Short description of error
When adding a Copy Rotation constraint to an object, the Add mode seems to not work correctly
(or at least how I would expect it to work). For example, setting the rotation of the object to (x,x,x) and
the target to (-x, -x, -x) does not consistently result in having no net effect. The value for which this *stops*
working is x >= 54.

Exact steps for others to reproduce the error
1 - Add an object, give it a rotation of (80, 80, 80), Euler XYZ (default)
2 - Add an empty, give it a rotation of (-80, -80, -80)
3 - Add a Copy rotation constraint on the object, and set the target to empty

The included bug.blend file contains an animation that goes over the values of x as described in the
above example from 0-100. The problem can be seen around halfway through the animation at the
critical value above.

Result
Object seems to have a weird rotation, which is not the expected outcome. The same happens
when only one of the axes is rotated more, and also when they don't necessarily add up to 0.

This has been tested on multiple Windows machines.