A mate ecently explained his process to me - he puts a long 4mm Allen key in the bolt head and heats the key with a butane torch. The heat transfers to the bolt and softens the threadlock and the bolts come out easily. I’ve not tried it myself yet but it sounds good, and he reckons it works well.
Ok but @maynardeames explained method suggests it's always the case. I'd hope that now and then you get the bolt out just by unscrewing...