Thanks especially to kstampy and SVoyager so far for providing such detailed descriptions for the targeting bug. This might seem silly to most, but it is quite valuable to us.
Due to our inability to reproduce the bug in-house, I am positive that it is triggered by playstyle nuance, as opposed to hardware or connectivity. The chain triggering of abilities for the Unclean Beast is a great clue that already seems to have pointed us in the right direction, according to the engineer looking at the problem. We are now looking at how issuing multiple identical commands overtop of an executing timed ability can possibly break a trigger.
Simple reason we haven't been able to reproduce this if that proves true? We don't normally power-mash the buttons when we play, most of us learned while building the game that it actually slows down the unit responses, but we should have anticipated what a really motivated overclicker can do.
I don't think this is the same root problem with Sedna, but getting so many good recordings of it occurring in game might reveal to us some patterns, as SVoyager has said.
In any case, this is great information for us, please keep it coming.