Cannot delete ACAD_PROXY_EN elements

Issue:
Cannot delete ACAD_PROXY_EN elements in the drawing. If you select all elements in the drawing and click DELETE, the ACAD_PROXY_EN are still visible. 
Solution: 

1. Copy all elements to a new drawing (drawing2). The ACAD_PROXY_EN will not be copied. 
2. Delete all elements in the first drawing. The ACAD_PROXY_EN will be visible. 
3. Use the command Select <enter> all <enter> and use command EXPLODE. An exploded copy of the The ACAD_PROXY_EN element will be placed above the The ACAD_PROXY_EN object. 
4. Use the command Select <enter> all <enter>, and copy these elements to drawing2. All but the The ACAD_PROXY_EN elements will be copied to the new drawing (drawing2).