They wish to change the law so that all prisoners (not just ones sentence to longer then three years) lose the right to vote. But the way they've drafted the bill means it will only apply to people convicted after the amendment is passed - thereby giving the vote back to any prisoners who are in jail for longer than three years! He suspects that this is not what they intended.
Geddis's post also makes a scathing attack on the Bill as an offence to democracy and civil liberties:
This proposal is downright wrong in its intent, outright stupid in its design and (if finally enacted) would be such an indelible stain on the parliamentary lawmaking process as to call into question that institution's legitimacy to act as supreme lawmaker for our society.
Further followup from Andrew Geddis.