Hi Eloy,
My unique and genuine interest it to see any fix, improvement landing back into "mother" Moodle. So everybody else benefits of it.
That's a totally reasonable request - to answer your question, yes we upstream all Moodle bugs found during development or reported to us. We have an 'upstream' tag in our bug tracker specifically to identify and track upstream fixes. When we file a new Moodle issue we usually supply a patch and respond to review input until the fix is integrated.
Aside from bug fixes we try to offer upstream anything we think would be useful, from whole features, minor improvements, security improvements, performance improvements, or even the occasional crazy idea . If there's anything else we've done that HQ would like to see in core Moodle, drop me a PM.
Finally can I also just say a huge thank you from the Totara dev team for all the hard work you and the rest of the community does to make Moodle the awesome platform that it is. Totara couldn't exist without it and we do appreciate it!
Simon