Too many songs (?)

[roystonsayswutt]

Hi, I've been subbed to Spotify for quite a while and I've reached close to 800 songs in one of my main playlist. I've realised that recently when i add a song into the playlist, it doesnt appear there unless i copy paste the entire playlist from 'Songs' to my playlist. 

A fix or explanation for this is greatly appreciated as this has been bugging me for quite a while. Thanks!