“Play next” means it will add a selected item from library to queue right after currently playing item, keeping current song playing, and so next will be played song which was added by “Play next”.
Actually there are similar “Add to queue” and “Clear and play”, but still different, because in this case currently playing song will not be stopped and it will save a lot of time by manual removing queue items.
Under the hood it should do:
Get current playing queue item position
Remove all items after current item (optional)
Add selected items from library into queue after current item
Yes, agree, it can keep existing items in queue and insert new items after current. But to me it should remove them, because for example, after playing newly added album, it will return to remaining songs of previous album which was in queue, which already became irrelevant.
As a work around.
In the settings under “playback options” if you set playback mode to single. When you tap on a song it will play and add only that song to the bottom of the queue.
Then you can use the “add to queue” option on all the next songs you want.
but it will add to the end of queue. It will not be played next right after current item. You have to manually remove all items between current one and newly added one at the end to simulate behavior of suggested “play next” functinality to play new item right after current.
And btw no matter in this case what playback mode is set, “continuous” does the same effect as you described.