This has already been answered here.
http://reactable.com/support/?qa=37/leaving-does-reactable-rcording-appear-forever-home-screens&show=38#a38
We have already submitted an update to apple that allows you to control this feature (playing audio in the background) and it's pending approval from them. You can also check this link (from apple) on how to close apps that run in the background
http://www.apple.com/support/iphone/assistant/application/#section_3
Best regards,
A