Mesh freezing in Spine is a feature that sets the rotation to 0 and the scale to 1 for the current vertex positions of a mesh. This is because a mesh itself does not inherently have rotation or scale properties; it only has vertices with specific positions. The rotation and scale values provided by Spine are for convenience, allowing you to manipulate the mesh similarly to other attachments.
When you use the Freeze button, it essentially resets the mesh's rotation and scale values to their default states (0 for rotation and 1 for scale) based on the current vertex positions. This can be useful when you have made adjustments to a mesh and want to set those adjustments as the new "normal" state.
However, freezing a mesh does not affect its parent bone or the keyframes associated with it. If you parent a mesh to a different bone, the deformation keys will still be relative to the original parent bone, which can cause issues if the new parent bone does not have matching keys. This is why your mesh appears modified when you change its parent bone.
To move your mesh without losing the correct keyframes, you should consider using weights to bind the mesh to bones. This way, the deformation will follow the bones' movements, making it easier to maintain the correct deformations even when changing parent bones.
For more detailed information, you can refer to the Spine User Guide on Meshes.
