It may just be a selection issue. Go to "options" and 'selection' tab. Make sure 'Associative Hatch' is un-checked. You can then continue to create associative hatches in you drawings but when selected the boundary objects will be ignored.
To disassociate an existing associative hatch from it's boundary, select the hatch and open the PROPERTIES manager. At the top it will say "All (2)". (See attachment.) From this drop down window select "Hatch (1)".
Now, under the second major element grouping below, "Pattern", find the Associative element and change the "Yes" to "No". This will disassociate the hatch from the boundary, and can now be erased without deleting the boundary, if desired. This technique can be used to disassociate multiple hatches from their boundaries in one action.