Fx3 supports bytes less than 512 for high speed. The error is specific to the host side. So the work around you found seems to be the only option as this is out of FX3's scope. Any device, other than FX3 would also face the same issue with those descriptors.
- Madhu Sudhan
Host is the motherboard Asus H170-PRO with installed Windows 8.1
I think this is not the worst set :)