Missed by many I suspect, so hat tip to Australia's Lowy Institute e-briefing:
The failure two weeks ago of GLONASS was frankly an unprecedented total disruption of a fully operational satellite constellation. At just past midnight Russian time (GMT + 4) on 2 April, every GLONASS space vehicle began broadcasting corrupt data. This rendered the system completely unusable to all receivers worldwide, and the system remained that way for about eleven hours.
The slim technical details:http://gpsworld.com/glonass-gone-then-back/

The US report and wondering about reliance on non-Russian GPS:http://www.atlanticcouncil.org/blogs...-backup-to-gps

Which has an interesting Crimea-related passage:
It should be no surprise that those unbadged Russian troops swarming into Crimea last month brought with them trucks with very recognizable GPS jammers. The new R-330 Zhitel system appears to have enough power to jam even military-grade receivers over a wide area, and a dispersed deployment of them could overwhelm even the most sophisticated electronically-steered antennas.
I note this failure was on the 2nd April 2014, after April Fool's Day.