Dragging a new guide from a rule activates the artboard behind the ruler
In a document with multiple artboards when I have an active artboard (black outline) and then go to drag a vertical guide from the left ruler, the measurements change and a different artboard gets selected that's running under the rulers. When clicking in the rulers any object, layer or artboard selection needs to be suspended.

-
Ah, I see now what you mean. Indeed, Ai treats a click on the ruler as focusing an artboard that is under the ruler.
Voted. -
David Burch commented
I am submitting this same issue. If I have clicked on an artboard, the ruler units will update to reference THAT artboard, but if even a sliver of the artboard to the left is visible in my Illustrator window and I select the vertical ruler to slide a guide over (to the right), the ruler updates to reference the artboard to the left. The only workaround seems to be ALWAYS repositioning the artboard I am working with to be the first visible artboard next to the vertical ruler.
I use the latest version of Illustrator per the date of this post.
-
Ryan, does it still happen for you?
It does not happen for me when I test it in recent versions, the rulers stay true to the currently active artboard. -
Philippe Galmel commented
No problem if GPU is Off.
1. Create a document with 2 art-boards,
2. Show rules and switch to art-board rules (Display/Rules/),Click on a rule when an art-board is under this rule, the art-bord under the rule become the active art-board. This is not the expected behavior.
On the other hand, the behavior is correct when GPU acceleration is off.