I thought I saw this one logged already, but my search-fu can't find it.  Just had this happen in the Cavern of Xaur Tuk-Tuk.  The chief is supposed to drop the Shimmer Scale shield, but when I killed him while under the effects of the bow he did not.  Not a huge issue in this case as I tend not to use that shield, but obviously a bit problematic overall (going to have to watch the drops carefully and won't in many cases know what I'm missing).  In case it matters the bow is not currently upgrad