Version 8.1.35
Ever programming in the Designer, moving objects around and after a while the copy/paste feature stops working? Send to back/move to front just disappears. The only way around this I have seen is to close the designer out and restart it. Happens almost every time I work in the designer for extended time: 3-4 hours.
I feel like every new version there are different things that vanish on me. I restart about 2 times a day. This only really happens when I do a ton of screen development all at once. If I am just adding bindings, scripts, etc. then I don't really have this problem.
I wonder if this is OS-related. I'm always running my designers in Linux, lots of different versions, and I just don't have these problems. At all.
Sadly windows is the standard for too many places.
Feels like a relevant thing to happen (I am sure it is a side effect of using Windows)
Along with random loss of ability to copy and paste, after a few hours I get screen tearing when resizing the panels. It just seems to stroke out every once in a while. 
FWIW, the loss of copy/paste etc in Perspective is a bug in the Designer I have seen and when looking into making a ticket for it, was told it may have been resolved with an update in 8.1.40. Often re-opening the resource: typically a view or window, fixes it
Since then I don't think I've seen the issue working in Perspective, but I think I've still seen it in Vision recently. If you are running into this issue while not working on a Visualization resource that would be a new problem to me.
We use Window's VMs for classes.
I have not experienced the loss of copy/paste -yet- in 8.1.44. However, lack of Send to Front/Back is still apparent.
In addition to closing & opening the view, I've noticed that I can sometimes 'get things working again' by deep-selecting different containers (especially a parent - or root container) before attempting Send to Front/Back.
I’m in 8.1.44 or 45 I think. The one thing I’ve noticed and maybe it is what the OP is talking about or maybe not. I will have the copy, paste, delete and duplicate not be selectable anymore in a view or across the perspective module. The fix for me has been running the view in preview mode then stopping it and the options come back.
I have experienced this copy/paste/duplicate issue in 8.1.44 and often have to close/reopen views to resolve.
