Bone axis indicator in 3d window bug?

I'm not sure if this is a bug but it was my thinking that the colored circles in the 3d window are assigned a bone and that when a bone is moved the circles should rotate.

If yes something is wrong with X axis (red) and Y axis (yellow). X axis is rotating the blue circle (for Z axis) and Y axis rotating the blue ( for Z axis) and red ( for X axis) circles. Z axis is working like I think it should and rotating the blue circle.

This is not a BUG. That's is how the posing in XNALara/XPS works.
BTW: The Y axis is working like anybody think it should. Rotating around the Y axis rotating the blue ( for Z) and red ( for X ) axis and circles. The axes of a coordinate system should always be perpendicular to each other. So rotation one axis should always turn the other two axes.
XPS use Euler angles. This result in a "Gimbal Lock"

Watch at 1:48



A well-known gimbal lock incident happened in the Apollo 11 Moon mission. On this spacecraft, a set of gimbals was used on an inertial measurement unit (IMU). The engineers were aware of the gimbal lock problem but had declined to use a fourth gimbal.
Some of the reasoning behind this decision is apparent from the following quote:
   "The advantages of the redundant gimbal seem to be outweighed by the equipment simplicity, size advantages, and corresponding implied reliability of the direct three degree of freedom unit."
   — David Hoag, Apollo Lunar Surface Journal

They preferred an alternate solution using an indicator that would be triggered when near to 85 degrees pitch.

   "Near that point, in a closed stabilization loop, the torque motors could theoretically be commanded to flip the gimbal 180 degrees instantaneously. Instead, in the LM, the computer flashed a 'gimbal lock' warning at 70 degrees and froze the IMU at 85 degrees"
   — Paul Fjeld, Apollo Lunar Surface Journal

Rather than try to drive the gimbals faster than they could go, the system simply gave up and froze the platform. From this point, the spacecraft would have to be manually moved away from the gimbal lock position, and the platform would have to be manually realigned using the stars as a reference.
After the Lunar Module had landed, Mike Collins aboard the Command Module joked "How about sending me a fourth gimbal for Christmas?"

In XPS, you can see this Gimbal lock by rotating the thigh bone -90°.
Now it becomes (almost) impossible to turn the thigh so that the toes point outwards. The Y axis and the Z axis lie in the same plane and both Y and Z rotations have the same result. One degree of freedom is lost.

The advantage of Euler angles is that the values ​​of the rotations are apparently intuitive. All angles set to zero mean "un posed". That sounds logical, but is mathematically wrong.
Try a (artist) mannequin.

Start from default pose.
--> x0 y0 ... The head points up. The noise points forward. (Default pose)

 Rotate now the head first to right (Y eq -90°). The head points up. The nose points to the right.
After this, nick the head down (X eq 90°). The head points to the right side. The nose points down.
--> x90 y-90 ... The head points to the right side. The nose points down.

Now take the rotation back in the same order. First Y reseted. Than X reseted.
First the Y axis. The head still points to the right. The nose points forward.
Now the X axis. The head points now to the back. The noise points to the right.
--> x0 y0 ... The head points to the back. The noise points to the right.
That is mathematically  right, but strange and not intuitive.

In XPS, if you reset x and y (or y and x), the result is always "posed reseted" eq "un posed". Mathematically wrong, intuitive correct.

That's why users like to pose the characters in XPS.
Everything works like designed. The circles show the (real) way which the bones will rotate along, if you rotate the axis.

Okay I get it.