Both the above shots were
taken with a Canon 5D. The image on the left was taken at 1/200
shutter. The right was taken with 1/160th
shutter. I used cheap wireless
sync system that I bought on eBay but have never noticed
this problem before. The shots are for my hotsauce website www.colibrihotsauce.com.
UPDATE
Is it the "cheap wireless sync" system that I bought on eBay? Maybe, a little. Below is a shot taken with a pc sync cord.
Shutter at 1/200. Not as bad, but definitely still shows the shadow of one of the shutter curtains.