Problem with playback after an change of Instrument

Maybe i'm doing something wrong but here goes. I had a Double bass in my score and changed it to Bass Clarinet. when i press playback every note played in the Bass Clarinet was sustained and wouldn't stop making the whole piece unlistenable. I have even tried adding, instead of changing the Bass Clarinet and the same thing happens. I hope i have explained myself well enough that you understand. I don't remember this happening before the last update.