You can turn these messages in Fatal messages that will abort ROOT and give you a traceback.
For doing this you just need to do before calling the integrator (making sure there are no others warning messages) gErrorAbortLevel = kWarning;
many thanks for the suggestion. It works for c++ but not for python at the moment due to this bug https://sft.its.cern.ch/jira/browse/ROOT-10566 . The proposed solution is surely usable in some cases but in some cases it is too cumbersome.
Is there any way how to have more control over warnings and errors originating from a given ROOT class? Does (new) PyROOT provide (or plan to provide) more control over the warning and error messages (see my previous questions)?