[Nagiosplug-help] check_http and string in content

[Robert Hebditch]

I've been exploring check_http plugin and it seems like finding and 
failing to find a string appears to be hit and miss

check_http -H foo.foobar.org -u / -s popeye -w 3 -c 5  does not fail 
when -s popeye not found
yet
check_http -H foo.foobar.org -u / -s popeye -w 3 -c 5 -S  returns 
CRITICAL string not found

Likewise
check_http -H foo.foobar.org -u /mat/mat.cgi -s soda and pop -w 3 -c 5 
-S  returns CRITICAL string not found
but
check_http -H foo.foobar.org -u / -s  beef and lamb -w 3 -c 5 -S does 
not fail appropriately

I've tried taking out the -u check when there is no need for it (ie when 
it's /) I've tried single/double quotes around text with spaces in it 
and I've tried changing -s so that I only look for one word.

 Other http AND https checks fail appropriately while others don't - 
basically the same syntax all the time

What  am I missing?