THANK YOU!!! I figured it was some setting somewhere. Odd that it defaults to "...and all subsequent"

The Play Now Action setting controls what is added on double click under Tools > Options > Playback Rules. It is set per Type.

I have used MM for years (since 2.0). Previously I could double click a song and it would be added to the Now Playing list. This made it easy to create playlists. Now when I double click a song ALL of the songs in the library are added to the Now Playing list. I have found that right clicking and selecting Play Next works, but it's not as efficient. Surely there is a setting that is wrong (maybe user error) that can be changed to correct this. TIA

Uncle Gary