Annotative objects such as text and dimensions in model space become annotative elements when a DWG file is opened in MicroStation. You can edit these elements and/or change the model's annotation scale. However, paper space annotation scale is disabled and annotative objects in paper space become non-annotative. This is because AutoCAD only allows annotation scale 1:1 for the paper space, no other scales are allowed. A viewport attachment has an annotation scale which is compounded with the traditional geometric scale to produce an annotation size in the paper space. Since MicroStation does not use this extra annotation scale on a reference attachment, currently viewports with arbitrary annotation scale value are not supported. However, a common practice of viewport annotation scale is to display texts at scale of 1:1 in the paper space so that they look the same. This is the same as turning on Use Active Annotation Scale on a reference attachment in MicroStation. So when your DWG viewport has a 1:1 effect of compounded annotation scale and custom scale, it will have the said toggle turned on and display correctly when the file is opened in MicroStation. In AutoCAD, this effect is achieved when a viewport's "Annotation Scale" and "Standard Scale" are shown equal.