Changing the environment variable DISPLAY will cause nodes to begin to rerun unnecessarily.
The 'environ' input claims to have differing values:

Error from a multisubject connectivity pipeline study (for a cmtk.Parcellate node):

" values differ in fields: environ: {'DISPLAY': ':1', 'SUBJECTS_DIR': '/media/Mobsol/subjects'} != {u'SUBJECTS_DIR': u'/media/Mobsol/subjects'}"

Removing:

display_variable = :1

from the nipype.cfg file fixed it.

Maybe we can work around this problem with a list of relevant environment variables (e.g. FSLOUTPUTTYPE, FSL_DIR, etc..)?