PyCharm overwrites externally modified jupyter notebook with an older version

After I updated PyCharm to 2017.3, a very sad feature (or a bug?) appeared:

if a jupyter notebook, belonging to some PyCharm project, was modified externally, PyCharm opens its local copy containing the old version and overwrites it.

It happened to me in two cases:

1. I closed PyCharm, opened the notebook in browser, edited it, saved. Opened PyCharm -- and there were no external changes applied, the notebook was in the same state as when PyCharm wa closed.
2. The project is located in the Dropbox folder, therefore all local project settings are synchronized. I opened PyCharm at machine_1, closed, waited for the Dropbox synchronization. Opened PyCharm at machine_2, edited the file, closed PyCharm, waited for the Dropbox synchronization. Opened it at machine_1, and no changes made on machine_2 and existing in the text version of the notebook file in Dropbox were seen. After I closed PyCharm, the notebook file lost all the changes made on the machine_2.