But it would indeed be a great help if a locked diagram was ... locked(!). And it should be a very minor and simple change in Sparx.
That's a diagram centric view not a model centric view. A diagram is a representation of a number of elements in the model. Elements that can belong to anyone, not just the creator of the diagram.
And it is MUCH easier to hide a connector that you can see than show a connector that you can't see. If you open a diagram and see that a new connector has suddenly appeared, that means that there is new information in the model that the person who created the diagram wasn't aware of. If it belongs in the diagram, great; if it doesn't, hide it. Better that than opening a diagram and not knowing if there is new information that may need to be shown.
You have right- user (like I) see what is "new" but:
- if someone delete relation from Repository, or change it betwen object - you can't see it. Someone, who want delete object or relation- can do it, even diagram are "Lock". When Object have "Lock" - yuo can still delete conect betwen him and other
- Sometimes We ( I & my group) doing diagrams with the same objects (difrent scope). On each of them we leave only few most important relation. But when I add new relation on second diagram I must still choose "Visiblity"->"Hide connector on other diagrams"- relation by relation... Or back on first diagram & hide all unnecessary.
In EA 14 We finally can Hiding many selected relations in one "Click" (Personally, I think that this is the biggest argument for switching to this version. Finally I can editing many relations in this same time)- But in old version user must do it connect by connect