Google play vs. the Nexus itself's apps

Many times I will go to Google Play, My Applications, and notice that several apps I own have updates. When I send those updates to the Nexus 7, they frequently get the error "application already exists" once they arrive. My question is, how does the Nexus 7's app versions get "out of sync" with the Google Play store? I've watched carefully and the store lags the actual automatic updates by several days in some cases. Google Play offers to update them for me when I know they've recently been updated automatically. What gives?

I have had delays but its only by few minutes. max 10 minutes and happens very rarely.
as soon as i update from PC or tablet it sync right away most of the time.

maybe the auto update is broken. I always manually update

Have you tried updating them from the Nexus 7?