The red armor right? Not the blue one?
That happened to me once - I got very excited and made superium armour, then realised that it was the wrong tier. That said, the title is correct so I suspect they have made the right stuff.
Just to cover some obvious ones: are you double-tapping jump, as you would to go into creative flight? Also, if you know how, I'd double check the config for Mystical Agriculture as I believe there is a setting that allows creative flight - if that's been set to "false" for some reason, that might be an issue.
A bit more info about what pack you're using might also be useful; I had a quick look and found an issue that Avaritia was causing back in June - it may be completely irrelevant, but I thought I should mention it.