Just an idea:
The privatekey in Wallet Import Format (WIF) is for example 'KwDiBf89QgGbjEhKnhXJuH7LrciVrZi3qYjgd9M7rFU73sVHnoWn' and contains 52 Base58 characters. The first two characters are always 'Kw', 'Kx', 'Ky', 'Kz', 'L1', 'L2', 'L3', 'L4' or 'L5'.
The Base58 alphabet = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz' and the 19th character is 'K', maybe indicating the beginning of the key.
When we create 100 privatekeys so we will have on average each Base58 character 86 times. But the first two characters starting with 'K' only 44 times and with 'L' only 56 times. That's approximately half of the rest of the characters in the key. That is maybe the reason for the LSB value of 19 being half of the others.