from the jeffrey friedl report:

The way (?i) works now is that if it appears anywhere 
in the regex, it turns on case-insensative matching 
for the entire regex. This is different (and less 
useful) than how Perl or Sun's Java package does it

[I'm pretty sure SRE does it this way to exactly
match the version of PCRE used in 1.5.2, but maybe
it's time to move forward... /F]