Hi.
This is happening with both locally installed WordPress and WordPress installed on a rental server.
Incidentally, this phenomenon is the same in both SSL and non-SSL environments.
I reproduced it by following the steps below.
1) Click “Add Row” button to add a row.
2) Open the “Edit Row” window and add Row Class to “Row Styles”.
3) Click on the left column area and close the pop-up window by clicking on the “Done” button while “Cell 1 Style” is displayed on the right.
4) Open “Edit Row” again and check Row Class in “Row Styles”, and you will see that the class name you set is gone.
