I've made the the database available

Thanks, I'll try to take a look at this today.

One strange thing ... Only after re-selecting the playlist would it show the correct number of songs.

This is correct. At the point you select a playlist, the FIDs contained in it are added (or inserted or whatever) to the running order. From this point onwards, the player doesn't know where they came from. This means that it won't spot any additions to the playlist. It also won't spot any deletions (unless you delete the track completely).