Have been messing around with solaris for a year or so, but this behavior seems new:

- Making a cube/box (or any other primitive) in solaris will show it subdivided/smoothed.

Bounding box will still be a cube. And it will render as a cube. But viewport will look like image provided.
As the LOPS viewport does not have an effect with "shift +" / "shift -" for viewport displacement I have no clue what is happening. The same behavior happens for everyone at our studio with 18.5.

Have I done something stupid?

I saw that the other day too. It looks like that release is broken. I checked the latest production build, and an earlier one and it doesn't occur there. So I guess don't use that version if you can.

Awesome! Thanks!