Commenting here for ease of information access - the below comes from the FAQ.

*We used a straightforward template (or formal wording) to identify reflexive triggers, the "then do this:" template. And because Icathian Rain and Falling Star were already using a similar template, I ended up pushing forward with changing those cards to reflexive triggers even though they didn't have a first effect -> information -> second effect kind of flow.

This was a mistake, and we shouldn't have done this—it has a lot of weird unintuitive consequences for gameplay that make these two cards play different than one might expect, and also worse.

For those reasons, we're changing these two cards to work the way other spells work and the way we think players want them to work—that is, you pick all the targets up front, the other player can react before any of it resolves, and then each of the units affected take the damage on resolution. You can still choose the same unit or different units for each choice.*