I've been playing around with your web version and I think there may be a bug with the way bits of entropy are calculated for the random word capitalization setting. It looks like enabling random capitalization about doubles the "full knowledge" bits of entropy calculated.

For instance, under the XKCD preset the passwords are calculated to have 81 bits of full knowledge entropy. Disabling random capitalization gives them 40 bits.

Randomly capitalizing words is equivalent to doubling the size of the dictionary they are chosen from. If you have a dictionary of 1024 words, each random word gives you log2(1024) = 10 bits of entropy. With random caps that increases to 2048 words and log2(2048) = 11 bits of entropy per word.

So a 4 word passphrase that's 40 bits without capitalization should only be 44 bits with capitalization, unless I'm missing something.