Submitted by cmichel
The LinearVesting.vestFor function (which is called by Converter) reverts if there already exists a vest for the user:
Theres an attack where a griefer frontruns the vestFor call and instead vests the smallest unit of VADER for the user.
The original transaction will then revert and the vest will be denied
There are several ways to mitigate this.
The most involved one would be to allow several separate vestings per user.
SamSteinGG (Vader) confirmed) 
