Okay, I did as you suggested with 8Player, and experienced the same result as I did with Glider: the playlist appeared in the 8Player “Playlists” folder, but inside the playlist only the first song is available. I guess with 8Player, it recognizes basic folders, so even without an m3u file, I can just group songs into different folders and play those folders on shuffle, with the same result as a playlist. As far as I can tell, so far Glider doesn’t recognize folders I create on the SD card, which was why I was trying to get the m3u approach to work instead.
Also, I should say, in my testing just now, I experienced quite a few major dropouts while playing with Glider, but am not experiencing them with 8Player. (I double checked, both apps were set to play directly from the Poly as server/renderer, bypassing the iPhone.)
Hope that’s helpful, perhaps there will be a fix eventually. I much prefer the Gilder UI and love that it allows control from the iPhone lock screen, which 8Player doesn’t, so fingers crossed.