Intel and XMir

Red Hat upstream most of their code. What they don't upstream is any of the work required to turn that code into an actual working release, which means the upstream releases of Red Hat-run projects are often unusable. Take for example PulseAudio - the latest version, 4.0, includes a patch that breaks resampling in a number of apps because it's half-baked and should never have been merged in that state. The (rather trivial) revert for this is upstream - mixed in with a number of other major changes that are inevitably going to cause their own regressions. There's no bugfix-only releases anymore.

Red Hat aren't affected by the fact all the upstream "releases" are actually semi-working code dumps - they employ the PulseAudio developers, and they effectively make the Red Hat packages into the real release by cherry-picking the safe patches and taking regressions seriously. (They don't necessarily upstream their patches promptly either - I've encountered at least one really obnoxious bug that was patched in the Red Hat packages by Lennart Poettering but not fixed in the upstream version.)