Can BPA lines be deleted?

One of our clients has raised an issue where they can't delete lines from a BPA using the Buyer Work Centre, as the delete icon is greyed out.  They are certain that this functionality has been available previously.  I was wondering if this may be new functionality that was introduced in the RUP's or Patch collections?  Or, is there a reason behind this functionality not being available, ie if PO's have been created against the BPA line does this then remove the delete function and only allow the line to be expired?

Any help is much appreciated!  Thanks.

Amanda.