HPBOUND system variable
Function Description:
The HPBOUND system variable is used to control types of objects created by HATCH and BOUNDARY commands.
Type : Integer 
Saved in : Not saved 
Initial value : 1 
Range : 0,1
System Variable Value:
0 : create regions
1 : create polylines
It will create polylines when the HPBOUNDRETAIN system variable is on.