On Twitter, we'd all better second-guess what we see in our friends list of tweets. Even if you want your public replies to be visible, be aware:
Or, when they can, they can't tell to which tweet you replied.
That's a lot like the Heisenberg Uncertainty Principle. That's where you can't precisely know a particle's position and momentum at the same time. You can know either one with high precision, but not both.
At Twitter, you can either see your friends' replies, or know which tweet they were replying to. But not both.
It didn't used to be like that. If we wanted to see our friends' replies, they'd simply show up in our list of tweets, with a handy link to the tweet it's a reply to. You'd see your friends' replies, and you could click-through to see what they were replying to.
That was nice. Twitter changed that. Now, the only tweets that show up in your list of friends' tweets don't have that handy link. So you can see that they replied to something, but you can't know for sure which tweet they replied to.
Keep that in mind when you want to reply to a tweet. You have a choice to make. If you want your friends to see your reply (isn't that the point of Twitter?), then you'd better type "@username" instead of click the reply-button under the star. Or, if you want your reply to be linked to the tweet it's a reply to, you should click on the reply-button under the star. You can't have both.
Having to make that choice sucks. Welcome to the HeisenTwitter Uncertainty Principle. This is why I like Plurk.