Sorry everyone for the confusion, as was mentioned, two of my previous emails was sent off-list for whatever reason. I read up on the topic arriving at the SE thread that was linked before [0] and tried to figure out the problem based on the work with strace, which I commended as very through and well-conceived. I also asked Roman to tell me whether group membership in `tty` would help, which own the files in /dev on my system. Also Roman, please note that many ioctls return data in pointers that can be passed to them which should be the spot where your results actually differ.
cheers! mar77i [0] https://unix.stackexchange.com/questions/117981/what-are-the-responsibilities-of-each-pseudo-terminal-pty-component-software.