I have a document with a rectangular box sitting over a picture using a drop shadow in InDesign. I have to export the PDF as a PDF/X-1a:2001 for the printer. However whenever I export the PDF using PDF/X-1a:2001 (compatibility Acrobat 4, 1.3) it puts a very small keyline on the picture around the shadow. This doesn't happen when you make it compatible with Acrobat 5. However it's then not PDF/X-1a:2001 compliant, so i need to find a way to stop it making this keyline while being Acrobat 4 compatible. Any tips of how to stop this keyline?