grep / strange behaviour of -i in conjunction with -o

[websafe]

Hello,

I'm using grep (GNU grep) 2.5 on Linux Slackware 10.2.
I've noticed the following:

---------------------------------------------------------------------------

# echo "blah blah http://zupa.InFo blah" \
        | grep -E "((http|ftp)[s]?)://([a-zA-Z0-9\.\-]*\.){1,}(info)"

## returns NOTHING, as expected. OK.

---------------------------------------------------------------------------

Next (added -i)

# echo "blah blah http://zupa.InFo blah" \
        | grep -i -E "((http|ftp)[s]?)://([a-zA-Z0-9\.\-]*\.){1,}(info)"

## returns, as expected:
blah blah http://zupa.InFo blah

---------------------------------------------------------------------------

BUT (added -o):

# echo "blah blah http://zupa.InFo blah" \
        | grep -i -o -E "((http|ftp)[s]?)://([a-zA-Z0-9\.\-]*\.){1,}(info)"

# returns NOTHING, but I've expected to see "http://zupa.InFo"; as the result.

---------------------------------------------------------------------------

It seems, that in conjuction with -o the option -i gets "turned off"
or sth. Am I thinking wrong or is this some kind of bug/feature? ;-)


Kind regards
websafe