Transferring Styles between (identical) Themes

I’ve come across a further bug in this customizing of themes issue.

I can no longer change the theme styles for ThemeFlood’s Black Theme. The changes - e.g. to Background don’t stick.

The every helpful Will can’t reproduce it and tentatively attributes it to a (known?) preview bug in RW 7 (I have 7.0.2). And that different Themes may handle the creation and management of (custom) styles differently.

RM tech support - also doing a sterling job at what must be an unimaginably busy time for them - suggest that Themes can’t have their styles changed at all, and that it’s necessary to recreate them in circumstances such as the ones I’m hoping for some help with in this thread.

Does anyone else agree that, if we’re to work elegantly with Themes’ Styles, this really does need to be cleared up once and for all.