Rail construction behaves differently with unity button VS KB shortcut "U"

when building rails in planning mode: select a rail section by clicking any ghost rail part, brings up a UI window that shows build cost for the section of rail that includes the part you clicked. this UI window lets you click the unity button to expedite the construction.
BUG --> if I click the unity button in the UI window, the whole rail section is built. However, if I press the "U" key, only the part that was clicked gets built rather than the whole section.

While it might look like a bug or an issue to you, this is neither of them &
at most (in my opinion) it should be called as an "uintuitive feature".

That's because every tool, (like copy, cut, demolish, pause) works exactly like this
( e.g: if you click on a track piece with the copy tool, it only coppies the track piece
that you've clicked & not the whole segment it belongs to).

One might argue that it doesn't behave the same for transports
(a.k.a. belts or pipes), where it does select / work on the entire segment,
however every segment of transports always become 1 entity,
where as tracks don't do that & they stay split up into individual entities,
so this comparison doesn't work / isin't applicable.

All of that being said, I thought that one could just hold one of the modifier keys,
to have the tool just select the segment instead (either SHIFT or CTRL),
so maybe that just works like you'd want 🤷.

except that's not what I'm pointing to... Once you are inside the UI window of the unbuilt track, the uni button and the shortcut have different effects. None of the thing you mention even have a UI window.

Also, I'll add that all other unbuilt UI windows work correctly and does the exact same action, whether using the button or the shortcut key.

There's a shortcut key to "apply / change unity action" on the entity that the inspector of which is currently being focused?
That's interesting, I had no idea that was even a thing & yeah, that seems like a bug (assuming that I'm on the same page now).

yup, click the ghost, hit "U" and it builds. except the rails... ; )