Yesterday I got crazy with a very special behavior of two of our iMacs (running with the latest Yosemite).
If you open a browser Tab in Safari or Chrome on the first iMac, it automatically opens in the task bar of the second one (Screenshot).
I disabled the Safari Cloud-Tabs Service in the iCloud, but the sharing keeps on going (still after rebooting, activating and deactivating again).
Funnily enough, it doesn't matter which browser you are using. Opening a tab in Safari displays it with a "chrome remote" icon on the other computer.
Has one of you ever seen this feature? Both Macs are using the same iCloud-Address.
Btw: There is no Chrome "iCloud Tabs" Extension installed, but like I said this problem happens on Safari too.