On Windows, when opening any container or the inventory, the mouse is temporarily and invisibly moved to the first slot of the container (to match the keyboard focus?). For the inventory menu, this is the head equipment slot. The mouse hovered name of the item in the first slot is displayed, but it is displayed somewhere else, at the "real" location of the cursor (where it is drawn by Windows.)

This means that regardless of the location of the mouse shown on screen, a left click immediately after opening a container on inventory screen will pick up the item in the first slot of the inventory.

This behavior is fine for keyboard focus: the focused slot can be moved with the arrow keys. But it should not affect the mouse's left-click behavior. One pixel of mouse movement will reset the cursor back to it's "real" location, as drawn by Windows, and clicking works normally again.

I can't tell you how many times I have mistakenly pulled stuff out of chests accidentally in 1.19.51, just be clicking through a line of chests to see the contents.