Last step of tapeoout---sealring and dummy fill density

Hi everyone,
Can I ask a few questions concerning the last few steps of the tapeout. I am using TSMC 65nm PDK.
1. My LVS is all set without sealring. However, it reports errors when I added the sealring...It seems LVS recognize the sealring as some device. Is this my problem when I modify the seal ring or is it one of the TSMC bugs? Is there a sealring appnote I should read?

2. I added the Dummy OD_PO and Dummy Metals but some of the density error persists when I run DRC. Does this mean that I might set the M_fill deck wrong?

3. I exported my design with dummy fills into GDS file and re-run the dummy fill command. In theory, the new generated dummy GDS file should be empty. To my surprise, there are new dummy shapes generated. Is this normal?

Thanks
Al

1 - answered in the other topic. probably not important.
2 - that means fill failed. you have to inspect the zones where the violations are and identify the reason why.
3 - not meaningful since the first GDS didn't pass density rules to begin with.