The TInyClr documentation says:
Input events use interrupts (IRQs). Interrupts are only available on 16 pins at any given time. Of those 16 pins, the pin number must be unique. For example: PA1 and PB1 cannot both be used as interrupts at the same time. However, PA1 and PB2, or even PA1 and PA2, can be used simultaneously with interrupts.
When using a UART, does the RX pin consume an interrupt?
Does any other functionality consume interrupts? Such as PWM, I2C, CAN, etc…