Left-Clicking once with the Marquee and Lasso tools no longer deselects the current selection, and instead just makes a new single-pixel one. Making a new selection altogether just adds it to the current one, rather than deleting the other one. This behavior is identical to how shift+left-clicking with the tools was for me. Now, there is no actual difference between clicking and shift+left-clicking, like the program believes i’m constantly holding shift. The only way to deselect something is either by manually right-click and dragging across it or deleting it.
Aseprite 1.3.14.2-x64, Windows 10.