Robert,
I've done quite a bit of work with half duplex RS485 where you have a pin telling the tranceiver chip if it should operate in TX or RX mode.
If I do
Code:
TxRx = Tx   ' Switch tranceiver to TX mode
HSEROUT["Test",10,13]   ' Send data
TxRx = Rx  'Sitch tranceiver to RX mode
The last byte (13) will not go thru properly because the tranceiver chip is switched from Tx to Rx mode in the middle of it. I'm pretty sure you'll get the same thing when disabling the USART. It's possible though that a low oscillator frequency in combination with high baudrate "masks" the problem.

Tumbleweed,
TRMT is the correct bit, thanks for pointing that out!

/Henrik.