Busting on Evoker's Roll will give you -1MP/tick less on your own total MP refreshed; i.e. you do not actually lose MP, but if you have any Refresh-like statuses on you, these will restore less MP than normal. The deduction is applied only once to the total MP refreshed, not once for each individual Refresh-like status. (For instance, if you have Refresh, Ballad, and an Evoker's Roll Bust status, the bust status will only cause you to receive -1MP/tick less than normal, not -2MP/tick for having both Refresh and Ballad active.)