I think it would be more intuitive to have the topics come up in the search too. It may be more suited to Contribute > UX than Contribute > Bug as it perhaps can’t be considered ‘broken’, but I’ll let someone else make the call on that one. 
And, just as an added bonus workaround, you can also get the ‘Arrive at topic’ prepopulated by using the 
Share button at the bottom of the private topic and accessing the invites from there. 