The component geometry used to create blocks should be created with a layer of 0, and other properties (especially color) set to a BYBLOCK setting.  That way it will take on the properties of the layer it’s inserted onto, or the specific properties you specify in the properties dialog.

Failure to do this can mean confusion.  For example if you create your block geometry on layer BLOCKGEOM, then insert them on a layer like INSERTS, you will find that layer INSERTS cannot be purged, even though there are no visible objects (when the layer BLOCKGEOM is frozen).  In this case the invisible insertion point prevents the layer purging.

This variable is often set to off (value of 0) when it should be turned on.  Newly created polylines take on the status of this variable.  This can create many negative effects.  For example when a dashed linetype is applied to polylines having dense vertices, the dash may not appear at all as the mask is reset on each vertex.  A second example is text based linetypes, if the linetype generation is turned off the letters will usually read wrong on curve segments.

If you have existing polylines created while the PLINEGEN variable was turned off, you can use the PROPS dialog to turn the linetype generation back on.