Hi!
I've just tested partial scrap in ME6.1.4.35: the system has successfully split and scrapped 0.2 out of an SFC of qty = 1 and 0.5 out of another SFC of qty = 2.
So, please check the setup of partial scrap on your side. You can consult SAP ME online help and Nonconformance How-To Guide.
Regards,
Sergiy