So we still have a few places in the UI where we disable the gameobject vs using alpha. If you enable then disable a gameobject containing ui elements, it still renders. Disabling the canvas works correctly but all children still render when disabled.
this is 2017.3 release candidate.
We are also experiencing this problem and have an open case: 974720 using 2017.3.0f1 
I really hope that this gets resolved before it goes wide as it’s likely a common use case!
Yes, and on top of that, even re-enabling the object will still not cause its vertices to be updated - it is forever frozen in place. I posted more details and a demo here .
Thanks for the reports, and sorry for the inconvenience! We’re aware of the issue and working to resolve this as soon as possible.