I think you may have been hallucinating.
The shuffle mode in Rockbox will shuffle the music files in your directory (or playlist, etc.) and create an on-the-go playlist of shuffled tunes. It then plays the shuffled playlist "in order" from 1/31 to 2/31, to 3/31....with the tracks and total being from the playlist.
You may have randomized a folder of songs, then turned Shuffle off. That way, if it played track 9 first in its randomized playlist, it would display 1/31, but when you turn off Shuffle mode as it plays track 9, it would modify the information to display 9/31 and keep going in order from there (10/31, 11/31....).
You also may have experienced a momentary bug in your build, but that's the way it's worked for me the past four years.