--- Operating System, Graphics card ---

Windows 7 64 bit home premium.
Nvidia geforce 9200.

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

Error: blender 2.68RC1 r57908 windows 64 bit.

--- Short description of error ---

The Shape Keys panel, Specials menu.

When you press "Mirror Shape Key (Topology)", it sets the use_topology property.
When you press "Mirror Shape Key", it doesnt change the use_topology property, so if use_topology is still True, "Mirror Shape Key (Topology)" is used.

--- Steps for others to reproduce the error (preferably based on attached .blend file) ---

Attached: mirror.blend
Use "Mirror Shape Key" works.
Use "Mirror Shape Key (Topology)", "o vertices mirrored", sets use_topology to True.
Use "Mirror Shape Key", bug: It uses "Mirror Shape Key (Topology)".