Upon copy-pasting (Ctrl+C > Ctrl+V, not Ctrl+D) a mesh linked to a Blender Source Tools sphere armature and pasting it, one gets: The mesh one copied (expected and wanted), the armature (expected and wanted), and smd_bone_vis.001 (unexpected and HIGHLY unwanted), which is a mesh of the ball thing used for sphere armatures when importing stuff using the Blender Source Tools. Happens in a 64-bit Blender 2.74 Zip install over a 2.72b install using Blender Source Tools 2.5.0 on a 64-bit Windows 7, didn't happen in said 2.72b install with Blender Source Tools 2.4.1. smd_bone_vis.001 spawns with an origin point of 0 0 0.

Steps to reproduce:
Import SMD or DMX mesh, leave import settings at default
Select a mesh object
Ctrl+C
Ctrl+V

Edit: Also, yes, this also happens when copying a mesh from a Blend session saved in 2.72b, which is how I found out about it.