Copying Armature through Python

I’m writing an exporter, and I want to transform an armature to Y-Up coordinates without actually saving it back to the blend file.
So, here’s my transformation matrix:

conversionMatrix = axis_conversion(from_forward='Y', from_up='Z', to_forward='Z', to_up='Y').to_4x4()

I get the armature, copy it, and transform it for exporting:

armature = ob.find_armature()
# Export...

However, the actual armature in blender is transformed, 90 degrees, which would ruin the model if I were to save the file.
It seems like the armature isn’t actually copied. Is there something wrong with what I’m doing?

Blender 2.72b

StackExchange Question here:

was answered on SE