They behave like that and pretty much every user (past a couple months) knows that. When a person presses "like" they know that some of their followers will see that. It signals "this is interesting" publicly, what other purpose could it serve? People that follow you would like to see it, of course. If you don't like people's likes don't follow them.
That said, the feature has always worked for me - actually it works too well that I have to think before I use it. Because after setting it once, it seems like I never hear from that person again. So it feels like an unfollow for me. Maybe the functionality depends on how much you interact with the person on Twitter? I don't know. I don't interact with people much on twitter, so when I choose that option, I don't see any likes from that person ever again, and it feels like I see their tweets A LOT less often than desired.
1. Agreement with the tweet, directed at the author only.
2. A form of "bookmarking" tweets for later. It's no accident that for most of Twitter's life this wasn't called a "like" but a "favorite" (with a star instead of a heart symbol).
As for "some of their followers will see it" and "I don't know [how it works]": That is precisely the problem. Your timeline isn't determined by your choices and the choices of the people you follow. The "algorithmic" timeline also adds a lot of randomness and unwanted choices that you can't control.
That said, the feature has always worked for me - actually it works too well that I have to think before I use it. Because after setting it once, it seems like I never hear from that person again. So it feels like an unfollow for me. Maybe the functionality depends on how much you interact with the person on Twitter? I don't know. I don't interact with people much on twitter, so when I choose that option, I don't see any likes from that person ever again, and it feels like I see their tweets A LOT less often than desired.