You can be sure, there is a rigid testing procedure - first during the development cycle, then the beta version is released to the third party developers in the Apple Developer program, an Apple Seed testing by selected high level users, then finally the public beta test.
I am not even sure this is bug, but rather a poor design. Nowhere in the Photos User Guide does it say, that photos will be printed in the same order we select them. Apple's photo applications are having a bad track record with respect to preserving the order of selected items when adding them to albums or slideshows or syncing albums between devices. The developers do not seem to consider the sorting of the items to be important. We arrange the photos in an album in a logical order to tell a story, but when we drag them from the album to a book project, a slideshow, or a shared album or print them, they will be rearranged. Sending feedback is necessary to make the developers understand that the sort order of photos in projects is essential. In the first version of Catalina we could not even sort smart albums at all.