Hi,
When the the ResetFlag "switch" in the interrupt declaration is set to YES it tells the interrupt system to clear the interrupt request flag when returning from the interrupt service routine.

However, the interrupt request flag for the USART RX is automatically cleared by the hardware when you read the FIFO buffer (which is what happens when HSERIN execute) so there's no need to have the software to clear it as well.
I can't say if it's valid for all devices but on the 16F1825 for example the RCIF is read only and can't BE cleared by software so having the ResetFlag "switch" set to yes makes no sense.

/Henrik.