Sometimes when manually skipping a track or the next track starts the album art/track details do not get updated on the KitKat Lockscreen. Instead the previously playing track information is displayed.
Play a playlist/Album and lock the device. Turn screen on but leave the lockscreen displayed and try skipping to the next track in the queue. This is a sporadic bug and does not seem to have any related causes/triggers.
Unlock the screen, this refreshes the data for the track so that when it is locked again the details will show correctly.
Although Bluetooth A2DP is not officially supported, the same behaviour can be experienced with track metadata not correctly updating on a bluetooth stereo.
If you are having this issue, can you please post (where possible):
Make and Model you are running the app on
Android version and is it stock or a custom ROM (if you are unsure, then it's probably stock)
Your current Spotify version (Settings > About > Version)