I am currently using the release version, sadly I cannot copy down the constant error I keep getting. It only happens when I am in combat, so I cannot just stop and copy and paste while I am fighting. The only add-ons I am usung at the moment is the UI, wowpro leveling addon and TomTom. it is not a button that is missing, the only way to descibe what happens is that while I am fighting, the UI completly lags out, and I get like 10 error messages that there is a conflict with an addon... I have to quickly close the boxes so that I will not die when fighting. I will try and do the ultimate sacrifice when it happens again and see what I can come up with.
Try with just nUI and see if you get the same problem.
There has been a known problem with addons in general whereby opening the blizzard map while in combat will blame the first addon in the list jabbering on about the drop down menu. I suspect this is what you are getting but possibly due to the wowpro levelling addon as I believe that uses drop down menus or lists in its addon. I get the same problem with my questing addon occasionally but am unable to track down the cause as it is within the blizz menu / list system itself if I read the forum posts right about it.
To aid you in posting the errors you could try installing bugsack and !bugrabber to record the errors so you can look at them after the fight is over and copy and paste it into the thread.