It looks like your mana meter has a broken ceiling. Even when you hit your max capacity (the 'y' value), the system doesn’t stop 'x' from increasing. This "over-clicking" allows you to stockpile infinite resources far beyond what the UI suggests is possible.
When combined with an auto-clicker, this completely breaks the game economy. Since you can accumulate massive amounts of mana in seconds, the cost of upgrades becomes irrelevant, allowing you to buy out the entire shop instantly. Effectively, the resource cap is purely visual and provides no actual limit on your purchasing power.