Those of you who are interested in removing legacy execution behavior from your application please follow the instructions below:
Definition: Your application is expecting that all UserObjects and Postprocessors are also executed during initial setup without explicitly setting those flags (i.e. EXEC_INITIAL).
The most straightforward fix to removing this flag is to first find any input file in your test suite that contains UserObjects and/or Postprocessors and updating the
# before [Postprocessors] [./foo] ... execute_on = timestep_end [../]  # after [Postprocessors] [./foo] ... execute_on = 'initial timestep_end' [../] 
Once you've updated the execution flags to reflect the explicit times when those objects are executed you should turn off the legacy flag for this test by adding the following flag:
[Problem] type = FEProblem use_legacy_uo_initialization = false 
Once all of your tests are updated you can turn off the flag by updating your respective
ApplicationApp.C files. If you need assistance with this process, please contact the MOOSE team.
If you are using this flag it means that you are expecting the EXEC_RESIDUAL AuxKernels to execute at every possible execution time. Most of your applications do not use this flag. If you need assistance turn it off please contact the MOOSE Team.Share on Twitter Share on Facebook