MarkDuplicates Picard

Question

I am using Picard to mark only optical duplicates for which I read the manual of MarkDuplicates. My script looks like this

#!/usr/bin/bash
java -jar build/libs/picard.jar MarkDuplicates \
      I=sorted.bam \
      O=mark_opticalduplicate.bam \
      MAX_OPTICAL_DUPLICATE_SET_SIZE=300000 \
      TAGGING_POLICY=OpticalOnly \
      M=markedoptical_dup_metrics.txt

I am not sure I am getting only optical duplicates when I am using the samtool flag 0x400 Any suggestions at this point is highly appreciated.