Due to a bug in Apple's iOS, using the "maintain audio pitch" setting in speed effected clips can cause random playback sync issues and export sync issues. iMovie will display the same error given the chance.
Chris has come up with a way for us to completely avoid using the Apple code for this feature and we will be testing it starting today.
If you have a project that has audio sync issues, please contact us at email@example.com
so we can send you a beta build with the fix - not only will it solve your sync issue, you can do us the favor of helping to verify the fix.
If you are on the beta test already, please load 1.4.8 and test a variety of clips at various speeds using maintain audio pitch and mixed in a project with normal clips. Be on the lookout for playback sync as well as export sync.
Thank you all for your help!
UPDATE: We have fixed some issues, but there is still one sync problem that we are working on. Again, let us know if you have a project with sync issues.