When viewed within OpenBuildings Designer various shapes with a dense hatch applied display correctly, but when plotted to PDF the results are as shown here:
In this specific use case, modifying specific pattern attributes using the MicroStation Properties dialog resulted in the correct display when plotted to PDF:
Pattern Angle = 45 degreesLine Style = 0 (continuous)Line Weight = 31
While different cases may require variations, hopefully this will provide a good starting point.