It looks like a better strike to me. There was an issue with the 2006 cents that was a doubled die:
2006P-1DO-001
http://www.coppercoins.com/lincoln/...ie_state=mds
Here is a side by side of a normal and DO-001:

You can see there was a bit of a stronger difference that year on the DDO. But the term thickening was used and not a doubled earlobe. So I feel the 1999 is just a better strike of the coin. Not a doubled ear. Note on the last two images the difference in strength of the hair/beard areas. It is just a better strike.
2006P-1DO-001
http://www.coppercoins.com/lincoln/...ie_state=mds
Here is a side by side of a normal and DO-001:

You can see there was a bit of a stronger difference that year on the DDO. But the term thickening was used and not a doubled earlobe. So I feel the 1999 is just a better strike of the coin. Not a doubled ear. Note on the last two images the difference in strength of the hair/beard areas. It is just a better strike.






















