The latest version of the desktop app features a filter (Crtl + f) function that allows a user to filter certain tracks from the playlist and "bring them to the forefront." For example, if I filter my largest playlist (which is 3,000+ songs) for "Nirvana," Spotify presents the 68 Nirvana tracks I have in the playlist. If I play this playlist while it is featured, it will only play the 68 Nirvana tracks that I have filterd; regardless of being on shuffle or not, the playlist will not play any songs that are not based on the filter criteria.
I believe the functionality that I just described above is excellent and how the software is intended on working. However, in the Spotify mobile app for iOS, the filter functionality does not work like this. Using the filter function in a playlist will filter the presented songs based on the user's inputed criteria/query, however, the playlist that is being filtered will not restrict it's playback to the criteria that the user has inputted. For example, if I searched "Nirvana" on the same playlist above on my iPhone, the same 68 Nirvana songs that I have on that playlist would be presented to me. However, if I selected "Love Buzz" (one of the tracks), then placed the playlist on shuffle, then skipped to the next track, the playlist would then play one of the other 3,000+ tracks from the playlist; it would not restrict playback based on my inputted criteria/querry.
In summary, the filter function on the mobile app does not work propely in accordance to the way it works on the desktop app. I think most users who have large libraries would like the filter app to work similar to the way I described above.
What can we do to get the correct filter functionality implemented on the iOS app?