Some time ago we've added an option to keep current selected tool when switching presets - it is useful in some cases when you like to use presents for multiple tools at the same time (like big / medium / small / textured) - so going from small brush to big brush, then switching to eraser, and going from big eraser to small eraser.

That said, if you prefer old behaviour, all you have to do is to go to "Edit -> Application settings" and uncheck options as shown on the picture below.

Also, since this caused a lot of confusion, we're going back to the previous behaviour as a default option for new users.

so it replaces the selected preset with the current tool as if it were an empty preset even though there is an existing preset.