Lpc2000

I'm writing a driver for UART1 on a LPC2138. So far most things seems
to work (considering the crappy hardware capabilities). My current
problem is that I loose interrupts when receiving data.

I run the UART in 115200bps and my ISR takes care of all IRQs except
the modem status ones that are not enabled. If I send a block of a
couple of hundreds characters, sometimes one RDA IRQ is lost. I know
this because the missing data always are the size of the Rx trigger level.

The ISR reads the U1IIR once in the beginning, compares the register
data to the different IRQ types in priority order. The first matching
type is handled (and the IRQ resetted), the U1IIR is then read again
and so on. When no more pending IRQs, the ISR is exited. When a 

Am I missing something essential?