When writing with setting for register-true formatting and writing in a 
textframe, the raster for register-true starts with the vertical position of 
the textframe. So the raster for register-true is not the same in the hole 
document, but different for the normal page and each textframe.

You can workaround, when you work with a fix line distance for the reference 
style, then you can calculate the right position of the textframe by hand, but 
that's very unpractical.