events-page BUG of "Use Existing Gallery" from Gallery Block on Events Pages

I'm a v7.1 user. Let’s say I have an Events Page, I created a new entry, let’s call it “Day One”, then during the editing, I added a Gallery Block (Grid). Of course I can upload images from my local files, my main confusion here is on the right side of the “Upload Media”, there is an option called “Use Existing Gallery”, the question is where these Existing Galleries are? If I haven’t had one, where can I create one? 

I doubt this is a BUG, because this option will be always "There are no collections.”, and there is no way to pull from any collections here. Please confirm

I have uploaded a screenshot here

Thanks

I have this same question. Can someone help?