From Andrei:

if the object corresponding to the current key is deriving from TCollection it means that it was written with kSingleKey option so it has to be written after merging with the same option. Otherwise one gets weird results when merging lists of histograms.


git-svn-id: http://root.cern.ch/svn/root/trunk@23947 27541ba8-7e3a-0410-8455-c3a389f83636