Issue: The skill level-up buttons do not conform to normal button behaviour standards. Button clicks should only be processed if the mouse is still within the bounds of the button when released.
Steps to Reproduce: Move the mouse over a skill "+" button. Press the mouse button. Move the mouse outside of the button. Release the mouse. The button-click is still handled and the skill is increased.
This has been a long-standing gripe of mine. Other buttons may also exhibit the same flaw, but the immediate permanent game-impact of skill-ups make this the most egregious. Though it may seem like a trivial complaint at first glance, having such important buttons operate counter to established standards is a significant detriment to usability.