I did test on 
- Python 3.5.1 on Windows 64 Bit and 32 Bit (Machine A)
- Python 3.4.4 on Windows 32 Bit (Machine A)
- Python 3.4.3+ on Ubuntu 15.10 64 Bit (Virtual Machine on Machine A)
- Python 3.4.2 on Machine B and C
- Python 3.3.5 on Windows 32 Bit (Machine A)

I did test but not produce bug. (report 8 correctly)
- Python 3.2.5 on Windows 32 Bit (Machine A)
- Python 3.1.4 on Windows 32 Bit (Machine A)
- Python 2.7.10 on Windows 64 Bit (Machine A) 

Machine A: i7-5775C with Windows 10 (build 10586.36) 64 Bit
Machine B: http://www.tutorialspoint.com/execute_python3_online.php
Machine C: https://repl.it/languages/python3

Code are here

import io
with io.TextIOWrapper(io.BytesIO(b'.\r\n...\r\n\r\n\r\n')) as fp:
    fp.readline() # '.\n'
    fp.readline() # '......\n'
    print(fp.tell()) # 18446744073709551628 = 0x10000000000000009

Not only those string produce bug, also adding more dot make produce bug sometimes.