andy@MunchKelly:~/Builds/MWE$ python3 MWE.py

RooFit v3.60 -- Developed by Wouter Verkerke and David Kirkby 
                Copyright (C) 2000-2013 NIKHEF, University of California & Stanford University
                All rights reserved, please read http://roofit.sourceforge.net/license.txt

 *** Break *** segmentation violation



===========================================================
There was a crash (#8 0x00007fdfc58d05ce in SigHandler(ESignals) () from /home/andy/Software/ROOT/lib/libCore.so).
This is the entire stack trace of all threads:
===========================================================
#0  0x00007fdfc6752dff in __GI___wait4 (pid=275782, stat_loc=stat_loc
entry=0x7ffc5d28d138, options=options
entry=0, usage=usage
entry=0x0) at ../sysdeps/unix/sysv/linux/wait4.c:27
#1  0x00007fdfc6752d7b in __GI___waitpid (pid=<optimised out>, stat_loc=stat_loc
entry=0x7ffc5d28d138, options=options
entry=0) at waitpid.c:38
#2  0x00007fdfc66c20e7 in do_system (line=<optimised out>) at ../sysdeps/posix/system.c:172
#3  0x00007fdfc58d4ab6 in TUnixSystem::Exec(char const*) () from /home/andy/Software/ROOT/lib/libCore.so
#4  0x00007fdfc58d539b in TUnixSystem::StackTrace() () from /home/andy/Software/ROOT/lib/libCore.so
#5  0x00007fdfc5b3ef44 in (anonymous namespace)::do_trace(int) () from /home/andy/Software/ROOT/lib/libcppyy_backend3_8.so
#6  0x00007fdfc5b3efc1 in (anonymous namespace)::TExceptionHandlerImp::HandleException(int) () from /home/andy/Software/ROOT/lib/libcppyy_backend3_8.so
#7  0x00007fdfc58d9095 in TUnixSystem::DispatchSignals(ESignals) () from /home/andy/Software/ROOT/lib/libCore.so
#8  0x00007fdfc58d05ce in SigHandler(ESignals) () from /home/andy/Software/ROOT/lib/libCore.so
#9  0x00007fdfc58d8fea in sighandler(int) () from /home/andy/Software/ROOT/lib/libCore.so
#10 <signal handler called>
#11 0x000000000970bb00 in ?? ()
#12 0x00007fdfc58059dd in THashTable::GetHashValue(TObject const*) const () from /home/andy/Software/ROOT/lib/libCore.so
#13 0x00007fdfc5804bcf in THashTable::Remove(TObject*) () from /home/andy/Software/ROOT/lib/libCore.so
#14 0x00007fdfc5802027 in THashList::Delete(char const*) () from /home/andy/Software/ROOT/lib/libCore.so
#15 0x00007fdfc57596cb in TDirectory::Close(char const*) () from /home/andy/Software/ROOT/lib/libCore.so
#16 0x00007fdfc57217d9 in TROOT::CloseFiles() () from /home/andy/Software/ROOT/lib/libCore.so
#17 0x00007fdfc5721ea2 in TROOT::EndOfProcessCleanups() () from /home/andy/Software/ROOT/lib/libCore.so
#18 0x00007fdfb207e02a in ?? ()
#19 0x0000000000000000 in ?? ()
===========================================================


The lines below might hint at the cause of the crash.
You may get help by asking at the ROOT forum https://root.cern.ch/forum
Only if you are really convinced it is a bug in ROOT then please submit a
report at https://root.cern.ch/bugs Please post the ENTIRE stack trace
from above as an attachment in addition to anything else
that might help us fixing this issue.
===========================================================
#11 0x000000000970bb00 in ?? ()
#12 0x00007fdfc58059dd in THashTable::GetHashValue(TObject const*) const () from /home/andy/Software/ROOT/lib/libCore.so
#13 0x00007fdfc5804bcf in THashTable::Remove(TObject*) () from /home/andy/Software/ROOT/lib/libCore.so
#14 0x00007fdfc5802027 in THashList::Delete(char const*) () from /home/andy/Software/ROOT/lib/libCore.so
#15 0x00007fdfc57596cb in TDirectory::Close(char const*) () from /home/andy/Software/ROOT/lib/libCore.so
#16 0x00007fdfc57217d9 in TROOT::CloseFiles() () from /home/andy/Software/ROOT/lib/libCore.so
#17 0x00007fdfc5721ea2 in TROOT::EndOfProcessCleanups() () from /home/andy/Software/ROOT/lib/libCore.so
#18 0x00007fdfb207e02a in ?? ()
#19 0x0000000000000000 in ?? ()
===========================================================


Error in atexit._run_exitfuncs:
Traceback (most recent call last):
  File "/home/andy/Software/ROOT/lib/ROOT/__init__.py", line 113, in cleanup
    backend.gROOT.EndOfProcessCleanups()
cppyy.ll.SegmentationViolation: void TROOT::EndOfProcessCleanups() =>
    SegmentationViolation: segfault in C++; program state was reset