RooFit objects, like RooWorkspace, that are automatically loaded from the Cling command line seem to be reloaded on each use. This can have unfortunate, highly confusing, and ROOT5-incompatible side-effects, eg.
For large workspaces, the reloading can also be noticeable by the time it takes to read the object each time.
A similar effect can be seen with other RooFit objects (like RooArgSet or RooFitResult saved directly in the file, not in a workspace), but not with other ROOT objects (like TH1F or TTree).
The object is not reloaded if used from a copied variable, eg. "RooWorkspace* w2=w".
This was not a problem with ROOT5 (eg. 5.34.25).
This issue was originally reported by Marc Escalier on the ATLAS Statistics eGroup.
PS. the test workspace used here can be easily created with: