When a widget that has a retainer box is behind another widget that doesn't have one it will call it's onclick instead of the one in front of it in the UMG when clicked (see attached gif).
This behavior isn't present in 4.23.1.
Found in 4.24.1 CL#10757647
Reproduced in 4.25 Main CL#10868506
1. Create a widget (WBP_Main) that has a row of buttons (WBP_HeaderButton) and put a scrollbox filled with a buttons (WBP_ContentButton) underneath the row of buttons.
-WBP_ContentButton has a retainer box.
-Make sure that there enough buttons in the scroll box that you can actually scroll with it.
2. Create and add an instance of WBP_Main to the Viewport.
3. Scroll the box so a WBP_ContentButton and a WBP_HeaderButton are overlapping.
4. Click on the WBP_HeaderButton where they overlap.
Result: The widget with the retainer box is selected.
Expected: The widget without the retain box is selected.
Note: Attached are example projects for 4.23 & 4.24.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-86153 in the post.