We currently start processes using stdin=subprocess.PIPE by default. That typically works fine, but issue #4065 demonstrates it can cause problems with some processes. It would be better to use stdin=None by default. It would avoid problems like in #4065 and be the same as the default behavior of the underlying subprocess.Popen.

The problem with this change is that it can cause backwards compatibility problems. In most cases there's no difference, but in some case being able to write to the stdin of the started process can be handy. Our own acceptance tests use this functionality and it's possible/likely that also others are using it. We made stdin configurable in RF 4.1.2 (#4102) so if the pipe behavior is desired, stdin=PIPE can be used explicitly.

I think we can change this already in RF 5.0 because it's unlikely many users are affected and stdin=PIPE can be used explicitly. Because stdin=PIPE only works with RF 4.1.2 and newer, we may want to wait until RF 5.1, though.