Clients intentionally uploading corrupt data is becoming more and more of a problem. These days I often lose like 40mb on a 350mb file (despite using an ipfilter.dat). With popular files this is just wasteful and annoying but with rare files it's often a huge problem because you often don't have an aich hash set to minimize the damage.
The most straightforward solution is probably to just ban (repeated) uploaders of corrupt data. Mldonkey has been doing this since ages and emule does it since 0.44c. Would it be difficult to port the appropriate emule code?