System Information
Operating system: Windows 10 64bit
Graphics card: Nvidia 1060 6gb

Blender Version
Broken: blender-2.80.0-git.552b2287db86-windows64
Worked: 2.79

Short description of error
Using Ctrl+P >"Bone" or "Bone relative" to parent an object to a bone, shifts the position of the object, as opposed to how it worked in 2.79 or parenting an object to another object.

If you unparent to restore the object to the original position, and parent again to the same bone, it doesn't happen a second time, unless you parent the object to a different bone and the bug happens once again

Use this 2.79 file to test parenting the cube to the bones. And try the same in 2.8 to test the difference