[clamav-users] Funny --include-dir behaviour

[newcomer01]

this is hilarious, why this won't work?
>                 nice -n -20 clamscan \
> --include-dir="^/home/$SUDO_USER/.thunderbird/Marc/Mail/" \
>                 --recursive="yes" \
>                 --quiet \
>                 --infected \
>                 --alert-broken-media="no" \
>                 --database="/var/lib/clamav" \
>                 --log="/var/log/clamav/clamscan.log"
>                 #--move="/etc/clamav/virusevent.d/Mail"
this should scan only the included path recursive

But when i do this:
>                 nice -n -20 clamscan \
>                 "/home/$SUDO_USER/.thunderbird/Marc/Mail" \
>                 --recursive="yes" \
>                 --quiet \
>                 --infected \
>                 --alert-broken-media="no" \
>                 --database="/var/lib/clamav" \
>                 --log="/var/log/clamav/clamscan.log"
>                 #--move="/etc/clamav/virusevent.d/Mail"
it worked well.
Can someone explain what's the reason for this?
Oh and the var SUDO_USER is the whoami

regards,
Marc