Consider the part toolbar button for example, but this applies to all toolbar buttons, in particular those which feature any kind of dropdown.
Trying to click on the “split button” doesn’t work–it maybe triggers the dropdown one in every five clicks. The intuitive behavior is to be able to click on that to trigger to dropdown. It was previously unknown to me that hold-clicking was the intended way to trigger this, which is a frustrating UX failure.
Also, the hover styles of the button give the user the impression that the selection bounds are different (like, the text isn’t part of the highlighted area, and therefore doesn’t look like it’s part of the button). This means, if you click below the icon in an attempt to click the split button, you’re clicking the button instead–another frustrating UX issue.
Expected behavior
Ideally, this split button is removed entirely for a more intuitive option. If it wasn’t to be removed, the split button should be much, much larger and should trigger the dropdown when it is clicked.