I'm having the same problem. I don't think MZ is causing the problem. I'm on 1.6.1 and in the template demo it works fine. Yet in my project it lags until it's completely frozen. I actually think its the latest Visustella plugins. Because when I disabled them in my project, the lag dropped considerably. It still lagged but not bad, and it allowed me to actually close it. I can't even close the relationship window when the Core and Events Move plugins are enabled. I would rollback my plugin versions but I'm afraid of breaking the other scripts in this pack.
EDIT: I tried copying the original plugin files from the template demo and it's still lagging. Yet the demo itself doesn't lag. I'm puzzled.