I can confirm this bug on the most recent Mac OS X 10.10.2 Yosemite with Google Chrome 41.0.2272.89 and with Keynote, whereas neither Firefox 36.0.1 nor Safari 8.0.3 are affected.
All weights and styles of Ubuntu seem to be equally affected, not only Ubuntu-R.ttf
I can confirm this bug on the most recent Mac OS X 10.10.2 Yosemite with Google Chrome 41.0.2272.89 and with Keynote, whereas neither Firefox 36.0.1 nor Safari 8.0.3 are affected.
All weights and styles of Ubuntu seem to be equally affected, not only Ubuntu-R.ttf