That could be the reason. I have renamed /bin/bash version 3.2 to /bin/bash3 and copied /usr/local/bin/bash that I build myself to /bin/bash making effectively

That could be the reason. I have renamed /bin/bash version 3.2 to /bin/bash3 and copied /usr/local/bin/bash that I build myself to /bin/bash making effectively bash version 4.3 the default login and system shell. I started bash 3.2 from bash 4.3 so that could be the reason why it is not vulnerable as child process.