bwa flag error

hello - i'm trying to set the -e flag in bwa aln and it doesn't appear to change. normally when i edit the flags and hit enter, the stdout shows the updated parameter settings.

i type:

./bwa aln -o 6

and it prints:

Options:

     -n NUM    max #diff (int) or missing prob under 0.02 err rate (float) [0.04]
     -o INT    maximum number or fraction of gap opens [6]
     -e INT    maximum number of gap extensions, -1 for disabling long gaps [-1]

where the number in brackets after the -o option is what i've entered. when i do this for the -e flag, it doesn't change.

i type:

./bwa aln -e 5 and it prints:

Options:

     -n NUM    max #diff (int) or missing prob under 0.02 err rate (float) [0.04]
     -o INT    maximum number or fraction of gap opens [1]
     -e INT    maximum number of gap extensions, -1 for disabling long gaps [-1]

any ideas what's going on here? has anyone been able to successfully change this parameter? it's entirely possible i'm misunderstanding how something works. any help would be great.

thank you!

SH1