Victor Simon Duijff

Yeah, I realised that, just before you posted that. Thanks for clearing this up.

I've just tried combining speed IV and Slowness IV, you're still slower than before.
Edit: It seems slowness gives a higher debuff than speed gives a buff, is this correct? Is it supposed to happen?

Then, isn't it still a bug when it doesn't work above a certain level?

Try it with speed 10 and slowness 10, for me, I couldn't move