_metadata has bizzare behaviour in python 3.3
See this post: http://stackoverflow.com/questions/28041762/pandas-metadata-of-dataframe-persistence-error?noredirect=1#comment44479369_28041762

Users using python 3.3 are reporting that when "non _metadata" attributes are copied they propagate to the new copied dataframe.  Furtheremore, when persisting to json they are able to access _metadata and non _metadata attributes from the file when loading via read_json method even though the json file has no contents which leads me to believe data is floating around somewhere.  I can't replicate this on my system as I use python 2.7.5 my _metadata behaviour is consistent with my expectations (see the post).  Assuming there are no other issues I can think of easy ways to write helper functions for json and hdf5 to persist the _metadata however now it appears to me that there may be other things to look into.  This is my first ever bug report, am I a real programmer now?
