System Information
Linux bubastis 3.10.25-gentoo #10 SMP Thu Jan 30 22:17:35 UTC 2014 x86_64 Intel(R) Core(TM) i7-4800MQ CPU @ 2.70GHz GenuineIntel GNU/Linux
01:00.0 VGA compatible controller: NVIDIA Corporation GK107GLM [Quadro K1100M] (rev a1) (prog-if 00 [VGA controller])

Blender Version
Broken: blender-2.72a-linux-glibc211-x86_64

Short description of error

The Undo operation sometimes affects more than one previous operation. This can wreak havoc on the properties adjustment panel of an addon.

Exact steps for others to reproduce the error

Start with the default cube.
Make a linked duplicate (alt-D) and drag it off to the side.
Add an array modifier to the original.
In the mesh panel, use the [2] button to make a single-user copy of the mesh.
In the modifier panel [Apply] the modifier.
Undo.

Notice that the array modifier has been restored. (this is correct). Unfortunately, the mesh is no longer single-user (it undid an extra operation which is incorrect).