With PM123 1.40 the bookmarks in the context menu are no longer flat. They may be organizes in sub menus like with a web browser.
The recommended way is to use a playlist. Put the URLs of the Internet Radio Stations into this playlist. While playing a stream of this playlist the previous/next buttons change the program.
Since an internet stream usually does not end the playlist is never played as sequence of songs. Instead the current stream keeps playing until you force another one to load.
This will take the whole playlist as one item. So using previous/next does not propagate to the next entry in this playlist, but leave the sub list and continue in the parent playlist.
Clear shuffle enforce PM123 to play the first valid item in
the list of URLs although if the shuffle button is pressed in the main
window.
Force shuffle causes PM123 always to take a random entry from
the list of streams. This is effectively causes load balancing.
If in doubt chose clear shuffle.