Setting a custom css class on a mosaic grid row in the advanced editor should be disabled if the layout is not customisable yet.

[fredvd]

When I double click on a mosaic grid row in the advanced view (press alt) in the Mosaic editor, I can set a custom css class on the row.

When I close the input field, my class is listed in the bottom right of the mosaic grid row.

But when I save the layout and go to edit again in the plone toolbar. , my custom css class is no longer there.

Tested with plone.app.mosaic master using test-5.1.coredev.cfg (Plone 5.1.4.dev0, plone.app.mosaic 2.1.2dev0). Tested with Chrome and Firefox. The webbrowser javascript console shows no errors.

[fredvd]

And.. 20 minutes later I realise the underlying issue. It's possible to set the css class in the advanced view of the layout editor even if you haven't customised the layout first.

The css-class editing feature shouldn't be available as long as the basic content layout template is still in use and the layout hasn't been made customisable on the context.