oh a bug!
Code:

$short = "short"
$long = "a really long string"

? "looking for a short string in a long string"
? "instr = " + instr($long,$short)

?

? "looking for a long string in a short string"
? "instr = " + instr($short,$long)



Might want to move this post to the Beta forum since it does seem to be a bug