I copied and pasted this section below from the American Funds site

http://www.americanfunds.com/funds/returns/alphabetically.htm

"The share prices of all of our equity funds, except Capital Income Builder and The Income Fund of America, decrease when a dividend is paid. The share price of only one of our fixed-income funds, Capital World Bond Fund, also decreases when a dividend is paid."

Why don't they either all decrease in NAV when a dividend is paid or all not decrease in NAV when a dividend is paid?  Why only certain ones?