As shown below, in riot-web, replying to a reply shows some confusing UX:

In addition the the reply, which works as expected, there is also a > In reply to <user> with a quote line shown on top. Not sure if this is intentional, but benoit pointed out this is different than other riot clients and I agree that if it is intentional, it is more confusing than helpful as it's not clear anymore what exactly was replied to.