Hi!
I do had the same problem with syncing (app-specific google) passwords via keychain for multiple devices (mac Mini in the office, imac at home and macbook air):
the google password should be different for each devices, but keychain syncs them ... so only one device is working.
to stop syncing passwords between devices (but keep keychain-sync ON) following helped me:
*on each device:
-open apple mail -> settings -> Accounts
-select the google account in the list
-change to the 3rd tab "Erweitert" ("extended"? ... I have german osx!)
-uncheck the box "Accounteinstellungen automatisch erkennen und übernehmen" (??"Account settings auto-sync")
*then on each device:
-then create new app specific google passwords for each device and enter the pwd in the email app -> settings -> Accounts -> Accountinformations -> password
If you have multiple google accounts eg "company" and "private" ... you do need to create different app specific pwd for each google account and every device! and enter the pwd into the apple mail account settings.
hope that helps ... without turning off the keychain!
br, pat