If you want it to work for more than one click, double-click the paintbrush icon instead of clicking it. It will then remain active until you click the icon again. That much I have figured out.
What I don't get is how it decides, for example, which character styles to copy when you select a whole paragraph with mixed character styles. From a perspective of "what would be useful," I'd expect it to
not copy
any character styles, because it should be obvious that the user is interested only in the paragraph formatting. Instead, it arbitrarily chooses one, for example bold if there is one word in bold in the entire paragraph, and applies it to the paragraph you select to apply the paragraph formatting to, obliterating any character formatting it may have already contained. Not only do I fail to see the usefulness of that, but I simply can't follow the logic: "the model paragraph has one word in bold; therefore the user must want every word in bold in every target paragraph, regardless of any character formatting already applied"????
It never ceases to amaze me how Microsoft can occasionally come up with a halfway decent idea for a feature, and then completely ruin it in the implementation. Something is seriously wrong with their design-development process, because I'm sure the person who came up with the idea (or appropriated it from another software company) couldn't have envisioned it working this way.