Prevent autocomplete of addresses from gmail in android email application
I had exaclty the same problem. I use Sony Xperia Z with Jelly Bean 4.3

The solution that worked for me is like this:
1. Stop contact autosync of google account. 
2. Clear all data and cache of Contact Storage App.

After this Email app will not autocomplete with Gmail contacts.
 The drawback is that the native Gmail App will not autocomplete either.

In general I believe this should be fixed in the next patch for Android somehow to let me choose from which contacts I want autocomplete to pull.

Hope this helps

KS