thanks, I've seen that behavior and I noticed it's been documented when I was researching my problem. The discussion https://fmdev.filemaker.com/message/94625#94625 mentions a note from Devcon that you should avoid copying objects from one layout to a layout of a different theme.
I'm glad you reminded me I could insert an image to illustrate the problem. Here's my attempt to apply the "warm bronze" theme as an example. The layout mode vs. browse.
I paid FileMaker $45 to look into the problem and they discovered that if I unselected the "show grids", my theme appeared in the layout. It was actually a $45 well spent and they said that even though other files don't behave this way, the file is not corrupted. I don't understand how, but I'm glad that nothing comes up during recover and that I can continue to use the file
Thank you for taking a minute to share what you found out. I'm glad there was some kind of resolution.