When clicking on the gradient bar to add a color stop:

• it's impossible to add a color stop in proximity of the pre-existing start/end color stops — the "+" simply doesn't appear and clicking doesn't do anything (although I'm not sure if this is by design)
• when the "+" icon appears on hover the gradient bar, I noticed that the icon's position doesn't track perfectly the cursor. This behaviour is more visible as the cursor moves away from the middle and towards the left or the right of the gradient bar. It gets to a point where the "+" icon appears, but clicking with the mouse doesn't fire on the icon (because of its offset)

(originally reported while reviewing #41361 (review))