Pycharm vs Intellij + python plugin

I've been using Intellij with python plugin and have experienced a problem with refactors when a function arglist has parameters that set default values I've seen strange results at times where some arguments might get lost.   I haven't used PyCharm for much beyond very simple stuff and was contemplating moving my project to PyCharm to see if these refactors are more reliable.

Is PyCharm using something different that might make it perform refactors (or other things) more reliably than what Intellij + python plugin does.   Or is Intellij's python plugin exactly what is in PyCharm?   

Ultimately, I need to do development in other languages so Intellij is a single license that works for me but I might consider a second license in PyCharm if its environment is handling Python better than Intellij's python plugin.

And no I haven't submitted a bug about the refactor because I haven't got an exact test case.   I've hit issues with it a number of times when alterring signatures and didn't have time to interrupt work to look into it.   Never had these issues during the many years I refactored Java but understand the python is a different set of issues.