Setting PYTHONPATH=newdir:$PYTHONPATH causes an empty component to appear in $PYTHONPATH if it was originally unset. This empty component gets treated the same as ., and this may cause erratic behavior.
(In the case when I encountered this it was because the PYTHONPATH env var leaked into a Python submission, causing it to perform an incorrect import.)
Setting PYTHONPATH=newdir:$PYTHONPATH causes an empty component to appear in $PYTHONPATH if it was originally unset. This empty component gets treated the same as ., and this may cause erratic behavior.
(In the case when I encountered this it was because the PYTHONPATH env var leaked into a Python submission, causing it to perform an incorrect import.)