Not sure if this applies to all Vicious Blades, but in adding a Vicious Shortsword and rerolling until getting a Nat 20 discovered that the bonus +7 damage is not being applied to the damage roll. I compared this to a Scimitar of Sharpness and confirmed there that the +14 damage on a Nat 20 does get applied. So this does look like a bug.
Not sure if this applies to all Vicious Blades, but in adding a Vicious Shortsword and rerolling until getting a Nat 20 discovered that the bonus +7 damage is not being applied to the damage roll. I compared this to a Scimitar of Sharpness and confirmed there that the +14 damage on a Nat 20 does get applied. So this does look like a bug.
The dice roller is still in open beta testing and as such isn’t smart enough to do everything yet. Always double check your bonuses.
Creating Epic Boons on DDB
DDB Buyers' Guide
Hardcovers, DDB & You
Content Troubleshooting