Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 1060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 419.17
Broken: version: 2.80 (sub 64), branch: master (modified), commit date: 2019-05-14 02:37, hash: rB9c9081d9ef5b
This is a really minor issue and I'm only reporting it for completeness. It can probably be a low priority.
Short description of error
In Windows 10 (at least) when you hover over the application icon on the taskbar, it shows you a small version of the open windows for the application, and each one has a close box in the upper right. If you click the close box this way for a Blender window that does not have the focus, it does not react until you move the mouse off the icon. Other windows apps close immediately on clicking the [X].
Steps to reproduce:
Open Blender, dismiss splash dialog.
Click on an open area of the task bar to take the focus away from the Blender window.
Hover the mouse over the Blender icon on the task bar until the thumbnail view shows up (as in screenshot above).
Try to click the X in the upper right corner of the icon (turns red when you hover over it).
Note that nothing happens until you move the mouse pointer off of the thumbnail mini-window.