How Do I Submit A Good Bug Report?

Please, don't send direct emails to Stéphane Raimbault unless you want commercial support.

Take care to read the documentation at http://libmodbus.org/.

Be sure it's a bug before creating an issue, in doubt, post a message on https://groups.google.com/forum/#!forum/libmodbus or send an email to libmodbus@googlegroups.com
Use a clear and descriptive title for the issue to identify
Which version of libmodbus are you using? you can obtain this information from your package manager or by running pkg-config --modversion libmodbus. You can provide the sha1 of the commit if you have fetched the code with git.
Which operating system are you using?
Describe the exact steps which reproduce the problem in as many details as possible. For example, the software/equipment which runs the Modbus server, how the clients are connected (TCP, RTU, ASCII) and the source code you are using.
Enable the debug mode, libmodbus provides a function to display the content of the Modbus messages and it's very convenient to analyze issues (http://libmodbus.org/docs/modbus_set_debug/).

Good bug reports provide right and quick fixes!