Well there are tow things to try.
1 After exporting the DXF, open files in DS or AC and do a save. Now check in Tops.
2 Suppress the features you don't want and then export the DXF and check in Tops.
I am running Win7 64bit, SW2011 SP0 64 bit. Autocad shows the removed entites. On a WinXP 32 bit running SW2011 sp4, 32bit, the remove entities feature works fine, all the way into Tops. I will update my SP to 4 and try again.