I posted a thread about this before, but maintenance happened and then it was gone.
Having this in any class used in a blueprint or added to a level will prevent that blueprint or level from being able to be saved. So far, the only work around I know is to remove the property in code, make the changes in editor and save, then re-add the code. This is a very painful work around, especially since I continue to use more and more material instances, and I am wondering if anyone has found another solution to this. Any help is greatly appreciated.