Audition won't play while multi tasking?

Control of Audition is via the OS - it has to be. Since you've already established that Audition can be controlled by it when it is first opened, that demonstrates that there's nothing inherently wrong with Audition. If it was, then everybody would have this problem, and they don't. It therefore follows that something within the OS as installed on your computer must be causing this - it's a simple logical progression. If it's only happening with Audition, then there's a fairly good chance that something like a rogue .dll file is behind it - that's how the linkage works. If you uninstall Audition and reinstall it, then the correct C libraries and .dll files should be reinstated.

So I suggest that you try that first, and see if it resolves this issue.