I am also having this exact same problem and it is infuriating. And I am not seeing a quick download links to the previous version unless it was the last major version change and I don't want to go back that far. I am using a Creative Titanium X-fi PCI-e sound card with a Sandybridge chipset (2700k). My sound works fine in anything that isn't flash and I have also tested in multiple browsers.
I did just find a version of 11.2 on another website and installed it and fixed the issue. The sound quality is also much better. With the new version I can have my speakers manually mirror the stereo sound (which is a pain) but the bass and trebble sounded way off when it was going through flash directly. Definitely avoiding any flash updates for a long while now.