Affects Version/s: Minecraft 1.8.7, Minecraft 1.8.9, Minecraft 15w50a, Minecraft 1.10.2, Minecraft 1.12
Fix Version/s: Minecraft 16w32b
java version "1.8.0_91"
Java(TM) SE Runtime Environment (build 1.8.0_91-b15)
Java HotSpot(TM) 64-Bit Server VM (build 25.91-b15, mixed mode)
Microsoft Windows 10 Pro
10.0.15063 Build 15063
Screen Resolution 1366 x 768 x 60 hertz
When the Minecraft window is resized while still ingame (and the center of the window changes), the player will start to spin until a GUI is opened and closed. The player can still move the mouse / use the movement keys / place blocks, but they will spin while doing so.
The only way to resize the window while keeping ingame focus is by using the WindowsKey + ArrowKey shortcuts.
1. Move the Minecraft window to the left side of the screen with WindowsKey + Left. This will put the window fully vertically on the side, and will resize the window.
2. Put the mouse back into the Minecraft window.
3. Move the window back to the center with WindowsKey + Right.
4. You will experience this bug.
(For extra fun, run /effect @p minecraft:nausea before hand, but this is not needed).
I believe that the root cause of this issue is that the "Center of the screen" location that the mouse jumps to each tick isn't getting updated on screen resize properly, but the location that is used to compute the movement of the mouse is.