Yes. groov automatically opens any clicks to an external page navigation gadgets in a new tab. The thinking behind this is to 'protect' or 'preserve' the user from needing to reload groov when they need to go back to it.
Your groov just looks to see if its a groov page in the same project, if so, just switch to that 'URL', since the other groov box is not the same project, groov simply treats it as an external URL and not a groov page and opens it in a new tab for you.
At the moment there is no option in the works to change that behavior.
That said, if you are happy to use a plug in, take a look at this;
We have not tested it, but it seems to be what you are after.
KEEP IN MIND, every time you click back, you will need to reload the groov project. groov uses the browser cache to ensure that the pages switch quickly for the user, you are going around that concept. Your mileage may vary.
Lets know what you try and how your users find it.
I'm very interested in this use case.