May version came out yesterday, since then:
1) It is NOT POSSIBLE to make ANY CHANGE in "Options", the "ok" button greys out, and pop-up window just sits there.
2) Size of .pbix file keeps increasing every time "Save" button is clicked, even when there is very little to no actual data change
I tested the problem you described and everything works fine in my case. How did you update your Desktop? You can uninstall the previous version and install it by re-downloading the installer from download center.
Download Microsoft Power BI Desktop from Official Microsoft Download Center
If you report a change, it will have a corresponding cache, size becomes larger is very normal phenomenon. Unless you do not make any changes, then the size of the pbix file will not change.
Community Support Team _ Ailsa Tao