"project" options seems to apply to all instances of Rhino 6

it would nice to have this per-instance of rhino… to save inadvertent 3d lines

It’s an application setting.
There is only one installation of Rhino so only one place to store those settings.

If it was what we call “session sticky”, then every time you started Rhino it would be off.
It seems that would be even more confusing.

John, thanks for your response. It seems this change was made intentionall becausethis doesn’t happen in Rhino 5, which is why I’ve brought it up. Maybe there can be an advanced option to revert to the previous way of doing things.

I prefer the Rhino 5 behavior for the way I work, which involves having multiple versions of Rhino open at once. For example, a cad model or 3d from a client, which is often modeled very quick and imprecisely, and the model I am doing, which has to be precise. Currently I am working on cleaning up a cad file which has poorly drafted content and lines at various elevations (they thought it was 2d but it wasn’t). So I need project in that document. But at the same time I’m referencing and working on a 3d model in another file. Sometimes I might have 5 or 6 documents open for different projects or portions of the project

On the topic of things that do seem to be session sticky but shouldn’t beare changes to aliases, new toolbar buttons, which are often lost the next time you open Rhino. I never understood why this happens. When I take the time to customize a button, I shouldn’t be worried about which order I close instances to keep it from disappearing.

In RH6 you don’t have to worry. Changes to application settings are used in all sessions immediately after you exit the options dialog in one session. That wasn’t the case in RH5. There you had to exit Rhino to have the changes written to the registry. It seems like you now have discovered the pros and cons of each method. But you can’t have it both ways and the new RH6 way is likely here to stay…

I just created a toolbar button in Rhino 6. Opened another instance and the toolbar button is not there.

When Rhino closes, the changes to the toolbars are saved.
If another instance of Rhino is open, it will not get the change.
If the first instance with the change is closed first, writing it’s changes, and the unaltered session is closed after it, the changes the first instance created are overwritten by the last.

The last Rhino in the barn wins.