XPS 13 2015: Dual Monitor - 2nd monitor blanking off and on

Using my XPS13 2015 and Ubuntu 15.04.  The large 4k monitor I've been using for months started to randomly blank off and on again yesterday.  I didn't use the set up for a few days, but right up to Wednesday last week it was fine.  So perhaps a recent change?  Sometimes changing resolution and then back again fixes?  But not sure because it's so random.

uname -a
Linux crom 3.19.0-33-generic #38-Ubuntu SMP Fri Nov 6 18:18:12 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

sudo dmesg

[  244.451414] [drm:gen8_irq_handler [i915_bpo]] *ERROR* The master control interrupt lied (SDE)!

(many many times)

Seems very related to a bug on Ubuntu, so I added my two cents to that:

bugs.launchpad.net/.../1488719

Paul