--- Operating System, Graphics card ---
Win 7 64bit, GeForce GTX 550Ti

--- Blender version with error, and version that worked ---
error in svn r53476
also in official 2.65.0 (r52859)
don't know if it worked in previous versions.

--- Short description of error ---

There are two problems actually, but they seem closely connected.

1. Objects with Solidify Modifier, which are copied, lose the Material Index Offset in that modifier.
2. After copying/linking the Solidify Modifier itself to another object, the Material Index Offset is reset to 0.

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

Open the attached file (solidify.blend)

In the file, there is the object "Plane" with materials "yellow", "blue", and"red" assigned to data,
and a solidify modifier with Material Index Offset = 1, Rim = 2 (which makes the back surface blue, and the rim red).
There is another testing object called "Object" with the same three materials and no modifiers.

To recreate problem 1:

Copy (shift D or alt D) "Plane".
The Material Index Offset and Rim are reset to 0 in the new objects (all other modifier properties are maintained) so the rim and backside become yellow.

To recreate problem 2:

Select first "Object" then "Plane".
In the menu Object > Make Links > Modifiers.
The Solidify modifier is properly copied to "Object", except that Material Index Offset and Rim are reset to 0 again and the object remains yellow.