Reading the LPC11E6x datasheet shows two sets of U0_RXD and U0_TXD pins, one pair noting it works only for ISP and the other with no comment. The USART0 pin list doesn't comment on the two sets or what's different or the same between them, and neither does anything I could find in the User Guide. The 'ISP' pair are available for all sizes of package so you'd expect that to be the real global USART0 RXD and TXD... I'm confused, obviously.
What's the deal on these two seemingly identical sets of U0_RXD and U0_TXD pins?