This is expected behaviour. The player caches the bulk of the track that you're listening to, and the start of the next couple (depending on size/memory availability). If you skip tracks, there's generally enough cached to allow playback to start while spinning up the disk.
However, if you skip too many tracks, it's necessary to spin the disks up in order to get the data for the next one. This is probably what you're seeing.
If you go to the player configuration dialog in emplode, you can turn on the disk icon on the player. This will make what's happening more obvious.
Roger - not necessarily speaking for empeg
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roger