Underwater leaves growing during propagation?

I've been propping a couple leaves from my red rex begonia, and it's my first time water-propping a rhizomatous plant. It's been in water for about 7 weeks, but 2 weeks ago I moved this and some other props to a sunnier window to see if they root faster.

Today I noticed these lil leaves have started growing underwater?? I've seen new leaves sprout from the top when water-propping my cane begonia, but I've never seen anything except roots form under the waterline. This part of the stem has been underwater the entire time. I'm so fascinated by this! Is it at all normal?