Inverted serial output from PC
From what I expect the output of 0x50 sent via UART should be:
  
  0(start bit)0101 0000 1(stop bit).


While that would make sense, it's incorrect. Serial data traditionally transmits the least significant bit first, so the expected output is:

    0 0000 1010 1
Start LSB...MSB Stop


which matches with your oscilloscope trace: