I did examine myself and I did played it in one sit through in both cases. So basically I replicated a weird bug XD. Interestingly I found an other bug but I couldn't replicate it:
Double Gargax: Two bosses spwan and neither of them can sent you to the previous screen. This makes it easier to finish the boss. This was actually how I finish the game the first time. I don't know how it happened nor if it's replicable, but I'm just warning you if someone finds it again.
Another weird bug that I found out is that if enter the Boss and keep pressing the mouse button, you can drag the cursor behind the wizard. If you do, so now you can enter the boss and move around to dodge him. I did replicate this one and I suspect that it might be related to how I produced the Double Gargax bug.