Audio playback stops when clicking off Reason 10?

[TW1306]

The other day I temporarily set up an external synth and audio interface with Reason 10, however since then all audio playback completely stops if I click onto a different program while playing audio in Reason. This had never happened until after I set up the external interface, even though after using it I changed all settings back to how they were beforehand, including changing the audio card driver back. Weirdly the reverse is not true; I can play a youtube video in Chrome and then click back onto Reason and press play, and hear both at the same time.

I know it's a relatively minor thing but since I only have one laptop, it's useful to be able to listen to projects while doing other things. Does anyone know what might be the cause of this?