Hi there,
The button should still do what it's supposed to. You can verify that it works by going to Website Data under the Advanced tab.
(Settings > Safari > Advanced > Website Data)
If nothing shows up under Website Data, then the button does what it's supposed to. You can also check your history to make sure it works, but you can only currently do that from the Safari app itself, not Settings.
I have my own explanation below for interested minds, but my short answer to the question is yes, it seems normal. I can't actually remember a time where I haven't seen this behaviour, and I've been using iOS for many years.
As for why it gets highlighted again, I assume the software logic that Settings uses to grey out the button doesn't actually check if data can be cleared, only that the button has been pressed. So the button turning blue again doesn't indicate something can be cleared, it just turns grey the first time to let you know you've pressed it. I've tested this by reopening the Safari Settings page in airplane mode (because websites can't load offline), re-entered the settings page, and it still turned blue. It seems like this is a bug, as Apple's documentation states "When there's no history or website data to clear, the setting turns gray" (https://support.apple.com/en-us/HT201265). But it's such a minor thing, that as long as my history and website data get cleared, seems good enough.
If you want to report this as a bug, you can do that here (https://www.apple.com/feedback/iphone/). But given how minor this issue is, and the experience I have with Apple's bug reporting, I don't see this getting addressed any time soon, if at all.