Many DXF files contain block records. Using blocks, shapes can be defined once and used repeatedly throughout a CAD drawing. However, PIPE-FLO does not import the blocks portion of a drawing. Therefore, when you are importing a DXF file containing blocks it is important to 'explode' these blocks into simple objects.
This is particularly important if you are re-importing a DXF file that had originally come from PIPE-FLO since blocks will be present in an exported system.