Looks like the redaction process is shuffling the layers about. The garbled text looks like the OCR layer has been brought to the front.
I tried your sequence using Acrobat X Pro & found that the redaction process stripped off the OCR altogether, so it was necessary to re-apply it. This was the result:
flops backup-1_Redacted.pdf
Is your program set to auto-OCR (i.e. scan>>OCR>>Save As)?