Additional information (possibly helpful this time):
An additional factor in the audio buzz bug seems to be pan settings. On the problem clips (which are 6 channel adaptive) the "pan" seems to be set to "L" on the buzz inducing clips (those clips producing buzz when crossfades are applied). Setting the pan to center seems to eliminate the buzz. (Note that the "pan" control seems inactive or unresponsive in these cases, the value for the pan must be set to "0" by numeric entry.)
Edit: it seems that simply changing the pan setting somehow changes something that will stop the fade from buzzing - so if the pan is set "L" then centering it helps; if it is centered then setting it L or R will help.
This does not apply to all buzz producing crossfades.
Additionally, empty audio tracks are producing buzz in some cases (which i haven't been able to troubleshoot) - the buzz occurs only in one channel.
No acknowledgement or response from Adobe on this.