Interesting, I hadn't noticed that option. Mine is set to do an auto rebuild if the number is less than 100, which is probably the default. So that is probably what is happening. I save a new song, open the song picker and if there are less than 100 songs, then new song appears.

For the folders with more songs in, I'm not sure I would want it to do a rebuild every time I opened it. Doing a rebuild by hand usually takes 10s of seconds and I wouldn't want that delay every time I opened the song picker. Maybe I'll play and see how long it actually takes.

I would have thought it wouldn't be that difficult to just add a single song as part of the "save song" process or even a background rebuild. Something for the WIBNI list.