Polylines in AutoCAD are specified as a set of vertices defined by the user (or an external program). The default AutoCad behavior is to create a straight line between each vertex. Additionally, AutoCad includes tools for curve-fitting and/or "smoothing" to apply curvature to each Polyline segment when desired.
AGi32 version 19 includes improved support for curved polylines when compared to previous versions. However, at the time of writing, this functionality is not yet supported in all situations.
When AGi32 encounters a curved polyline that it cannot parse properly, the program will revert to the default behavior and process the polyline using straight-line interpolation.
For the most robust CAD import, it is best to model curved elements in AutoCAD using entity types that have native support for curvature, as opposed to polylines. Examples include, Splines, Circles, and Arcs.
Splines can be an especially attractive option due to their geometric flexibility and the ability to specify the import precision easily in the AGi32 CAD Import dialog.