One thing that we've noticed consistently for Wiki Education program participants since the "Publish" label rolled out is that it's extremely confusing in sandboxes, because users take "Publish" to mean "move out of sandbox to make a live article". We've had many cases where users lost their sandbox work because they tried and failed to find a Save button but they knew they didn't want to publish their draft to mainspace and so avoided that button. Many users in this situation assume that, since there is no "Save" button, their draft must automatically be saved (since this is how many other WYSIWYG editors work).
A terminology change — or some other design changes — that made it more clear that "Publish" for a non-mainspace page is not that same as "Publish to mainspace" would help a lot.
Why namespace is relevant
Based on what we've observed and talked with students and instructors about, it's definitely perceived differently in sandboxes vs mainspace. These users know that a sandbox is a place for drafting work that isn't ready to be "live" in the sense of being a normal Wikipedia. In that context, many users interpret "Publish" to clearly communicate the idea of "this is no longer a draft and will be published as a normal article". In an already-live article, "Publish" is harder to misinterpret.