Hello, I am starting to write extensions for Inkscape but I have problems understanding the coordinate system in my rotations. 
Attached are files with the GroupRotate extension. 

I'm trying to create a repeating pattern duplicating the selected paths (In the end, 12 patterns)

As an argument I enter the center of the rotation, when I test in a document of 200mm by 200mm it goes well:

But when I test on a 400 * 400 document, a translation is added to the rotation. I do not understand why...

 

The two test svg files as attachments

I think it is because when you resize the page, a transformation is applied to the <g> layer, however there is no transformation on the page itself.

So if you calculate from the page dimensions, it does not take account of the transformations on the layer into which the object is inserted.