While recording a demo of section styles with 6.6 beta 1, I noticed that while I could change the variation in Styles, the changes would update on the front end of the site but would revert in the editor after hitting save. Here's a video showing front end vs back end:

Here's the demo video I was working on for good measure:

Here's the theme.json:

	"styles": {
		"blocks": {
			"variations": {
				"Dark": {
					"blockTypes": [
						"core/group",
						"core/columns"
					],
					"color": {
						"background": "#1e1e1e",
						"text": "#FFF"
					},
					"elements": {
						"heading": {
							"color": {
								"text": "#FFF"
							}
						}
					}
				}
			}
		}
	}

I am assuming this is likely because I'm adding an element style to the variation (button in this case) but that doesn't explain why the Heading doesn't update. This could very well be user error but wanted to report just in case cc @aaronrobertshaw