See https://sourceforge.net/tracker/?func=detail&atid=102435&aid=2728605&group_id=2435 for original report.
It seems highly unlikely to me that the bug is not in MSYS' cat.exe for the following reasons:
- Bug occurs with both cmd.exe and Cygwin's bash.exe.
- Filemon shows that MSYS-1.0.11's cat.exe is writing 1107 bytes which is already one byte too many.
- Bug does not occur with MSYS-1.0.10's cat.exe (Filemon shows that it's only writing 1106 bytes).
- Bug does not occur if MSYS-1.0.11's cat.exe processes a single 1106 byte input file containing both a.txt's and b.txt's contents such that the output sequence would be the same. The input data needs to be splitted into two files for the bug to occur.