UART(1) immediately after initialization is sending 1 byte (0x00) on top of data

[Colateral]

Connect LopY with 1 Arduino (or other UART device )

from machine import UART
uart = UART(1, 9600)
uart.write(b"Test")

received 5 bytes
[0x0] 'T' 'e' 's' 't'