Operating System: Windows
Pretty sure this doesn't happen in Linux.

Behavior summary

When focusing the window with a mouse click, all characters are highlighted up until the character clicked on.

Expectation

The window is simply focused, no extra selection occurs.

Extra

This is especially irritating in combination with #2050.
(selection: save_to_clipboard: false doesn't seem to work, resulting in pasting half the terminal screen back into the prompt)