I ran your awk's and got the output printed in the attachement.
I doubt the script replaces something else too 
[LEFT]sample attachment with -vet i/p file.
you can see these extra appended characters.[/LEFT]
I don't think awk copes very well with random control characters. But tr does:
tr '\000\032' ' ' <file >replaced
Otherwise, you could try something like gsub (/[\000\032]/, "") but at least mawk simply doesn't cope with nulls.