Grants the effect of Dualcast upon casting any spell with a cast time. While under the effect of Dualcast, your next spell will require no time to cast. Effect is canceled upon execution of any action other than an ability. Auto-attacks do not cancel effect.

It is atleast not a bug, it is intended like this. It is a lore reason in the end, you can find points for it and against it. So whatever.
I think it is fair, a redmage should do what a redmage should do. If you fcked that up, you deserve that loss of a dualcast. You can sprint and use potions 1gcd before it and it would have been all fine, if you really have to use them between it, then you failed something anyway.