Hi welcome on avast community 
Well ‘‘why?’’ I can’t tell you the answer, I guess is for security reason, to not allow inexperienced users to make dangerous input.
One thing I do with these FP, I submit them to virus@avast.com, and usually takes about 1 day, to get you answer back via email. Avast team working quite fast to solve these FP.
Regards RealNature,