--- Operating System, Graphics card ---
Ubuntu 12.04 - Nvidia 8600

--- Blender version with error, and version that worked ---
r60988

--- Short description of error ---
If I duplicate an object with a modifier "Mask" in Armature mode, the new object modifier "Mask" appears in Vertex mode

--- Steps for others to reproduce the error (preferably based on attached .blend file) ---
1. Add a Cube.
2. Select the Cube and add a Mask modifier.
3. Change the Vertex Mode to Armature Mode.
4. Duplicate the Cube.
5. Review the new cube modifier, not same.